KISS Notes Patterns in Nature

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keep it simple science

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What is this topic about?

To keep it as simple as possible, (K.I.S.S.) this topic involves the study of:

1. LIVING CELLS & THEIR STRUCTURE

2. CHEMICALS MOVE IN & OUT THROUGH MEMBRANES

3. NUTRITION IN PLANTS & ANIMALS

4. GAS EXCHANGE & INTERNAL TRANSPORT

5. CELL DIVISION FOR GROWTH & REPAIR

but first, an introduction...

Cells

All living things are composed of microscopic “lumps” called cells.

Some organisms are composed of just a single cell. All familiar organisms are made of many cells; for example, your body is composed of approximately 300 billion cells... you are “multicellular”.

Each cell is a tiny sac of “protoplasm”... water with a complex mixture of chemicals dissolved in it, plus many structures called “organelles” (little organs).

Plants and animals have cells with a few important differences. Organisms such as fungi are different again, while bacteria have a totally different cell structure.

Organization of a

Multicellular Organism

A building is not just a pile of bricks, and an army is not just a rabble of soldiers. Each has a structure, and levels of organization so everything works together.

Similarly, your body is not just a big heap of cells. It has levels of organization...

a

CELL

is the basic unit of any living thing.

A number of similar cells working together is a...

TISSUE.

(e.g. muscle tissue, bone tissue.) Various tissues are combined to make an...

ORGAN.

(e.g. heart, kidney, liver.)

A number of organs work together for a specific purpose. This forms a...

SYSTEM.

(e.g. digestive system.)

Finally, all the body systems working together form...

YOU -

a functioning, multicellular organism. In this topic you will study the basics

of the structure and functioning of living things.

GENERALIZED DIAGRAM OF A LIVING CELL

“Membrane” on the outside contains the cell , and

controls what goes in or out

Organelles

Cytoplasm is a jelly-llike liquid which fills the

cell

Preliminary Biology Topic 2

PATTERNS in NATURE

Cell

Division

Vital

Body

Systems

Cell structure

&

Chemistry

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Structure

of

Membranes

Diffusion

&

Osmosis

Surface Area

to

Volume Ratio

Photosynthesis

&

Respiration

Structure &

Function of

Leaf

Plant &

Animal

Cells

Reasons for

Cell Division

PATTERNS

in

NATURE

Living Cells

&

Their Structure

Chemicals

Move In & Out

Through

Membranes

Nutrition

in

Plants & Animals

Gas Exchange

&

Internal Transport

Cell Division

for

Growth & Repair

Cell

Organelles

Gas

Exchange

in

Animals

Circulation

in Animals

Gas

Exchange &

Transport in

Plants

Mitosis

Digestion

in

Animals

Cell

Theory

Cell

Chemicals

CONCEPT DIAGRAM (“Mind Map”) OF TOPIC

Some students find that memorising the OUTLINE of a topic helps them learn and remember the concepts and important facts. As you proceed through the topic,

come back to this page regularly to see how each bit fits the whole.

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1. LIVING CELLS & THEIR STRUCTURE

The Cell Theory

The “Cell Theory” is one of the fundamental concepts in Biology. It simply states:

• All living organisms are composed of cells or are the product of cells. (e.g. viruses) • All cells are produced from pre-existing cells. The evidence supporting the Cell Theory has come almost entirely from the use of microscopes to examine living things.

Our knowledge of cell structure and function has developed as the technology of microscopes advanced over the last 300 years or so.

Initially, only light microscopes were available, but since the 1930’s electron microscopes have revealed more detail of cell structure and function.

Comparison: Light & Electron ‘Scopes

Light Electron

Microscope Microscope

How the beam of light beam of electrons

image focused by focused by magnetic

is formed glass lenses fields

Magnification generally about up to 1,000,000 X

500 X. (500 times more

Maximum powerful)

about 2,000 X

Resolution about 0.2 μμm about 0.0002 μμm

(ability to see (1,000 times better

fine details) detail)

micrometres (μμm) 1 μμm = 0.000001(10-6_)metre.

1 micrometre is 1_/

1000of a millimetre

How Big Are Cells Anyway?

Typical Plant Cell

50-100 μμm

Typical Animal Cell

5 - 20 μμm

Bacterial Cells

1 - 5 μμm

History of Our Knowledge of Cells

Robert Hooke, 1665

Hooke is credited with being the first person to see cells and

name them. Using a primitive microscope, he looked at a piece of cork (dead tree bark) and saw tiny “boxes” like the rooms and compartments of a gaol or monastery. (hence “cells”)

Anton van Leeuwenhoek, 1676

van Leeuwenhoek used a very simple microscope, but it was equipped with an excellent lens, through which he saw living micro-organisms swimming around in a drop of water.

Over the next 150 years, microscopes improved, and it was suspected that cells were present in all living things.

Robert Brown, 1827

Brown was the first to discover structures inside cells. He discovered and described the nucleus inside plant cells.

By about 1840, the “Cell Theory” was becoming accepted by most biologists, because cells were observed in every organism studied. Louis Pasteur’s discoveries showed that infectious diseases were caused by “germs”, which were microscopic, cellular organisms.

Rudolf Virchow, 1859

and Walther Flemming, 1879 Between them, these two German scientists clarified the process of cell division, by which cells produce more cells. This established the principle that all cells come from pre-existing cells.

In the 20th century, the electron microscope opened up our knowledge of the fine detail of cell structures and their functions.

SSCCAALLEE:: 110000 μμmm ((00..11 mmmm))

Sketch of Hooke’s microscope

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The Major Differences Between Plant & Animal Cells

Plant cells have a tough CELL WALL on the outside of their cell membrane. Many plant cells contain a large VACUOLE.

Animal cells rarely have vacuoles, and if present they are small. Many plant cells contain CHLOROPLASTS.

These are green in colour because they contain the pigment chlorophyll. Chloroplasts are the sites of PHOTOSYNTHESIS, where plants make food.

Note: not all plant cells have chloroplasts... for example, cells in the underground roots cannot photosynthesise, so do not contain any chloroplasts.

What the Electron Microscope Reveals

The superior magnifying power and resolution of the electron microscope has given us a much more detailed knowledge of the cell and its organelles. The diagram below is a sketch of a plant cell similar to the one above, but with the added details that the electron microscope has revealed.

The extra organelles shown are generally NOT visible with a light microscope.

Generalized

ANIMAL CELL

Small Vacuoles (if any at all)

CELL WALL (outside of membrane) CHLOROPLASTS (green colour) NUCLEUS CELL MEMBRANE CYTOPLASM Cell Wall Cell Membrane Vacuole Chloroplast internal structure

Stacks of flat membranes (grana) contain the

chlorophyll Mitochondrion. Site of cellular respiration Lysosomes Golgi apparatus Nucleus

Extra detail revealed Endoplasmic Reticulum

A network of membrane structures connected to nucleus & extending throughout the cytoplasm

The tiny Ribosomes are often attached to the E.R.

Cell Organelles Visible with a Light Microscope

You may have done practical work in class to use a light microscope to view cells in living things.

Generalized

PLANT CELL

Large VACUOLE

There are probably no actual cells which looks just like these.

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The Organelles... Structure & Function

Nuclear membrane with pores, for

RNA exit Nucleolus RNA manufacture Nuclear material “chromatin”. (Chromosomes unwound and spread out)

NUCLEUS

The Nucleus

This is the control centre of the cell.

Inside the nucleus are the chromosomes

containing DNA, the genetic material.

There is often a nucleolus present. This is

the site for production of RNA, a

“messenger” chemical which leaves the

nucleus carrying instructions to other

organelles. The nuclear membrane has

holes or “pores” to allow RNA to exit.

Mitochondria

(singular: mitochondrion)

This is where cellular respiration occurs

Glucose + Oxygen Carbon + Water + ATP

(sugar) Dioxide

The ATP produced by respiration carries

chemical energy all over the cell to power all

the processes of life. The mitochondria are

therefore, the “power stations” of the cell,

converting the energy of food into the readily

usable form of ATP.

Inside a mitochondrion is a folded membrane

with many projections (“cristae”). This

structure provides a greater surface area,

where the enzymes (control chemicals) for

respiration are attached in correct sequence

for the steps of the process.

This structure helps the organelle

do its job more efficiently.

Inner membrane folded into “cristae” with respiration enzymes attached

Endoplasmic Reticulum

(E.R.)

E.R. is a network of membranes which form channels and compartments throughout the cytoplasm of the cell. Its function can be compared to the internal walls of an office building which divide the building into “rooms” where different operations can be kept separate so that each does not interfere with others.

The E.R. structure provides channels for chemicals and “messengers” to travel accurately to the correct locations, and for chemical production to occur in isolation from other operations.

This structure helps cells function

Often found attached to the E.R. are the tiny

Ribosomes

. These are the sites of production of proteins, the main structural and functional chemicals of living cells. RNA “messengers” from the nucleus attach to a ribosome to make the specific proteins that the cell needs.

ENDOPLASMIC

RETICULUM

RIBOSOMES attached to membranes Membranes Membranes enclose channels and “rooms” MITOCHONDRION

Outer membrane

The Cell Membrane

This is not only the boundary of the cell, but also controls what goes in or out of the cell. This is

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The Importance of Membranes

Except for the tiny ribosomes, all the cell organelles are built from,

and surrounded by, membranes.

The membranes

provide:-• the infrastructure of the cell.

• channels for chemicals to move through.

• packaging for chemicals which need to be stored.

• points of attachment for chemicals (“enzymes”).

• control over what moves in or out of each

organelle, and in or out of the entire cell.

The “membrane-bound” organelles help the cell’s various functions

to be carried out with greater efficiency.

Having these membrane-based organelles is the defining characteristic of

the “Eucaryotic” group of organisms, which includes all plants and animals.

Bacterial cells do NOT have all the membrane-type organelles,

Chloroplasts

Chloroplasts are found only in

photosynthetic plant cells. The electron

microscope has revealed that the

chloroplast is not just a bag of chlorophyll,

but has an organized internal structure

which makes its functioning more

efficient.

The “grana” are stacked membrane sacs

containing chlorophyll, which absorbs the

light energy for photosynthesis. This

light-capturing step is kept separate from the

“stroma” zone, where the chemical

reactions to make food are completed.

CHLOROPLAST

Double membrane envelope Membrane stacks (“grana”) containing chlorophyll “Stroma” zone

The Golgi Apparatus

is a semi-circular

arrangement of membranes which are

concerned with packaging chemicals into

small membrane sacs (“vesicles”) for

storage or secretion.

One type of “vesicle” produced by a Golgi

Body is the Lysosome. These membrane

sacs contain digestive enzymes which can

destroy any foreign proteins which enter

the cell.

Lysosome enzymes also rapidly digest the

contents of a cell which has died, so that

your body can clean up the remains and

replace the dead cell.

GOLGI BODY

Curved

membrane sacs Vesicles pinch-ooff for storage or secretion Lysosomes form this way

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Worksheet 1

Cell Theory & Cell Structure

Fill in the blank spaces and diagram labels.

The “Cell Theory” states that

(a)... are composed of

cells, and that all cells are produced from

(b)...

Our knowledge of cells is due mainly to the

technology of (c)...

The (d)... of a

microscope refers to its ability to

distinguish fine details. The

(e)... ‘scope is far superior

in both (d) and (f)...

The man credited with being the first to see

cells was (g)...

Label the parts of this plant cell seen with a

simple light microscope.

List 5 additional organelles normally only

visible with an electron microscope.

(p)...

q)...

r)...

s)...

(t)...

Complete these lists to describe the

functions of the organelles.

Organelle

Function

Cell membrane

(u)

(v)

Partitions cell into

channels &

compartments

Golgi apparatus

(w)

(x)

Cellular respiration.

(y)

Photosynthesis

Cell wall

(z)

(h)...

(i)...

(j)...

(k)...

(m)...

(l)...

(inside (k) WHEN COMPLETED,

WORKSHEETS BECOME SECTION SUMMARIES Practice Questions for this section

are included in Worksheet 3

Which TWO parts of this plant cell would

definitely never be seen in an animal cell?

(n)... and

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The Chemicals

That Cells Are Made From

CARBOHYDRATES

include the sugars and starch.

monosaccharides (mono = one)

are simple sugars such as glucose C₆H₁₂O₆

disaccharides (di = two)

are sugars made from TWO monosaccharides joined together, such as “table sugar” (sucrose).

polysaccharides (poly = many)

are huge molecules made from thousands of sugar molecules joined in chains or networks. Examples are:

Starch... made by plants, to store excess sugar. Glycogen... made by animals, to store sugar. Cellulose... made by plants as a structural chemical. The CELL WALL of a plant cell is made from cellulose.

Uses of Carbohydrates

Sugars are energy chemicals. Glucose is made by plants in photosynthesis, and is the “fuel” for cellular respiration to make ATP to power all cells. Starch & Glycogen are polymer molecules used to store sugars as a food reserve. Starch is the main nutrient chemical in the plant foods we eat. Cellulose & Lignin are polymers of sugar used by plants structurally. Cellulose makes the tough cell wall of all plant cells. Lignin is a strong material

2. CHEMICALS MOVE IN & OUT THROUGH MEMBRANES

INORGANIC CHEMICALS

These include small simple

molecules like water (H₂O) and

carbon dioxide (CO₂), as well as

mineral ions such as calcium, nitrate, phosphate, chloride, etc.

Although these are often considered of lesser importance, you should remember that all living

things are 75%- 95% water.

Polysaccharide. Small part of a Starch

molecule

PROTEINS

are the main structural chemicals of organelles, cells, bone, skin & hair.

Life is built from protein.

Proteins are polymers, made from amino acid molecules joined in chains.

Amino acid

molecules Part of a protein molecule...a chain of amino acids

LIPIDS

are the fats and oils. All cell membranes are built from

lipid & protein.

Lipids are used as a way to store excess energy food. Carbohydrates can be converted

to fat for storage.

NUCLEIC ACIDS

(DNA & RNA)

are the most complex of all.

DNA is the genetic information of every cell. RNA is the “messenger” sent out from the nucleus to control all cell

activities. DNA is a huge polymer of sugars, phosphate and “bases” coiled in a

ORGANIC CHEMICALS

“Organic” chemicals are based on the element carbon, which can form chains, rings and networks and so build the very complex molecules needed to make a living cell.

Many are “polymers” made by joining together many smaller molecules.

There are four main categories to know about...

Monosaccharide sugar

molecules

Disaccharide sugar

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Identifying Chemicals in Tissues

You may have done laboratory work to learn some simple chemical tests which identify important substances. These tests all rely on a “reagent” which changes colour.

To keep it simple (K.I.S.S.), learn these:

Cell Test Colour in Positive

Chemical Reagent Pure water Result

Glucose Benedict’s pale blue yellow or

solution orange

Starch Iodine yellow dark blue

solution brown or black

Protein Biuret blue purple

You will have used one or more tests on living tissue and examined the cells with a microscope. For Example: if tissue scraped from a fresh potato is mounted on a slide with a simple “contrast stain” (like methylene blue) the cells look like this:

If a drop of iodine solution is added, the same cells change as shown:

Once you have an understanding of the main chemicals that cells are made from, you need to realize that all of these substances, or their raw materials or waste products, are constantly moving in or out of a living cell.

TO DO THIS

CHEMICALS MUST CROSS

THE CELL MEMBRANE

The Structure of the Cell Membrane

The electron microscope and other modern analysis methods have revealed the structure of the membranes which surround a cell and form most of the cell organelles.

The membrane is extremely thin; just two molecules thick. The basic chemical unit is a “phospholipid” molecule; a lipid (fat) with phosphate groups attached. Each molecule has two distinct ends; one which is attracted to water molecules (“hydrophilic”) and the other is repelled by water (“hydrophobic”).

“Hydro”=water. “philic”=to like. “phobic”=hate / fear.

Two layers of phospholipids form each membrane. The molecules cling to each other, and line up with their hydrophilic ends outwards. The water-loving ends are attracted to the watery environment both inside and outside the cell.

Their hydrophobic ends are repelled from the watery surroundings, and cling together inside the membrane itself.

It is like a thin layer of oil floating on water. It is fluid and flexible, but clings together forming an unbroken “skin” on the surface.

Other molecules are embedded in the phospholipid bilayer. They are mostly proteins, many with carbohydrates attached.

These other molecules have various functions:

• “receptors” for messenger chemicals.

• identification markers, so your body knows its own cells from any foreign invaders.

• to help chemicals get through the membrane.

POTATO CELLS

POTATO CELLS WITH IODINE Organelles faintly visible Cell walls

Organelles turn black This indicates the presence of starch inside the organelles

(these are storage vacuoles) Membrane proteins O Onnee pphhoosspphhoolliippiidd hhyyddrroo--pphhiilliicc -pphhoobbiicc

MEMBRANE STRUCTURE

Outside of cell Inside of cell Double layer of phospholipid molecules

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How Chemicals Pass Through Membranes

The cell membrane as the boundary of a cell is a bit like growing a plant hedge as

the boundary of a field. It stops the cows and horses getting out, but a mouse,

or a lizard, can easily crawl through it.

Similarly, a membrane is “semi-permeable”; it prevents most (especially large)

molecules getting through, but allows others to pass through easily. Small

molecules like water (H

₂

O), oxygen (O

₂

) and carbon dioxide (CO

₂

) pass freely

through the membrane like a lizard through a hedge.

To understand how this happens, you must learn about the processes of

DIFFUSION & OSMOSIS.

Diffusion occurs in every liquid or gas

because the atoms and molecules are

constantly moving. The particles “jiggle”

about at random in what is called

“Brownian motion”. (Named for its

discoverer Robert Brown, the same man

who discovered the cell nucleus.)

Imagine a water solution containing a

dissolved chemical, but it is NOT evenly

distributed... it is more concentrated in one

place than elsewhere. As the molecules

jiggle about at random, they will

automatically spread out to make the

concentration even out. This process is

called DIFFUSION.

In a living cell, there is often a

“concentration gradient” from the

outside to the inside of the cell.

For example, because a cell keeps

consuming oxygen for cellular

respiration, the inside of the cell usually

has a low concentration of O

₂

dissolved

in the water of the cytoplasm. On the

outside, there may be a lot of O

₂

.

DIFFUSION DRIVES MOLECULES

THROUGH THE MEMBRANES

along the concentration gradient.

DIFFUSION of SMALL MOLECULES into a CELL

If the molecules can cross the membrane, diffusion will cause them to move from

higher to lower concentration. Higher concentration outside cell Lower concentration inside High concentration Lower concentration Equal concentration throughout To start with, the dissolved material is

not evenly distributed.

Diffusion causes the dissolved solute to

spread out uniformly.

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Osmosis

Osmosis is a special case of diffusion, which occurs when the concentration

gradient involves dissolved molecules or ions which CANNOT

get through the membrane.

The opposite situation can also happen.

A cell’s cytoplasm contains many

dissolved chemicals. If the outside

environment around the cell is more

watery (less concentrated in dissolved

substances) then osmosis will cause

water to diffuse inwards.

This can cause cells to “pump up” with

water and helps maintain their shape. It

can also cause problems for organisms

living in fresh water environments.

For example, consider a cell which is

surrounded by a solution containing a lot

of dissolved sugar. The sugar cannot

diffuse through the membrane to equalize

the concentrations. In such a situation,

water (which can go through the

membrane) will diffuse toward the high

sugar concentration, as if attempting to

equalize by diluting the sugar.

In this case, the cell will lose water and

might shrink and shrivel up. This can be

a problem for animals living in salt

water.

Sugar cannot get in through the membrane

OSMOSIS

Water diffuses OUT of cell H₂₂O H₂₂O H₂₂O Dissolved chemicals cannot diffuse out...

...so water diffuses into the cell.

This is how plants absorb water into their roots, even when the soil seems almost dry.

H₂₂O H₂₂O H₂₂O High concentration of sugar outside cell

Comparison of Diffusion and Osmosis

Diffusion is the movement of dissolved chemicals from an area of higher

concentration toward a lower concentration area. The movement follows the

“concentration gradient” of the molecules in question.

Osmosis is a special case of diffusion. It is the diffusion of WATER

through a semi-permeable membrane, against the concentration gradient of solutes.

It occurs when the solutes cannot penetrate the membrane, but the water can.

Other Ways Substances Get Through Membranes

Diffusion and Osmosis are vitally important for many chemicals (especially water) to get in and out of cells. Diffusion and osmosis happen automatically and without the cell having to use any energy. We say these are “passive transport” processes.

What about all the other important chemicals which cannot get through the membrane? Many proteins, carbohydrates and other molecules regularly move into or out of cells. How do they get in or out?

Cells have other ways to deliberately move substances across the membrane apart from diffusion and osmosis. One such process involves the membrane proteins carrying things. These “other” ways to transport materials across membranes require the cell to use energy (ATP from cellular respiration) to move substances. We say these are “active transport” processes. You do not need to know the details at this stage.

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1 unit

sides 2 unitsides

3 unit sides

Surface Area:

Six squares, each 1x1 SA = 6x1x1 = 6 sq.units Volume = lxbxh = 1x1x1 = 1 cu.unit Ratio of SA to Volume SA/V = 6 / 1

SA = 6

vol

Surface Area:

SA = 1.5

vol

Cells must feed their Volume,

through their Surface Area

The Importance of the Surface Area to Volume Ratio

Why are cells so small?

The answer requires a mathematical study...

Consider this series of cubes of increasing size:

But, all cells have to get whatever they

need in through their cell membrane, and

the size of the membrane is all about

surface area.

As any cell gets bigger, it becomes more

and more difficult for it to get enough

food, water and oxygen because its

SA/Vol. ratio keeps shrinking. Getting rid

of waste products also becomes more

difficult.

Large cells are impossible... all

single-celled organisms are microscopic, and all

larger organisms are multi-cellular. The

only way to be big is to have lots of small

cells.

Notice that as the cubes get larger:

• Surface Area increases, and...

• Volume increases, but...

• SA / Vol Ratio DECREASES,

because the volume grows faster

than the surface area.

This pattern is the same for any shape...

as any shaped object gets bigger, the

ratio between its Surface Area and its

Volume gets smaller.

What’s this got to do with cells?

The amount of food, oxygen or other

substances a cell needs depends on its

volume... the bigger the cell, the more it

needs according to its volume.

Surface Area:

SA = 2

vol

Surface Area:

SA = 3

vol

4 unit sides

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Fill in the blank spaces.

Simple, small molecules and ions (e.g.

water, nitrate) are known as

(a)... compounds, as

opposed to “organic” compounds which

are based on the element (b)...,

and

include:-• (c)... which are

polymers of amino acids

• Lipids, which are found structurally in

the cell (d)... and

are also used as (e)...

...

•(f)... which

include the sugars & starches.

One of this group, glucose, has chemical

formula (g)... and is the

“food” made during the process of

(h)... It is also the fuel

for (i)... (organelle) to

make ATP.

• Nucleic acids, of which (j)...

is the best known.

If Benedict’s solution turns from blue to

yellow, this proves that

(k)... is present.

Protein can be identified by

(l)... reagent, and if

starch is present iodine solution will turn

from (m) ... to (n)...

The cell membrane is made from a

double layer of (o)...

molecules, with various proteins

embedded.

The membrane is said to be

“semi-(p)...”

Diffusion is a process where molecules

move from a place of

(q)... concentration,

towards a (r)... concentration.

Osmosis is the diffusion of

(s)... molecules only,

against the solute concentration

(t)..., when the solute is

unable to get through a membrane.

Diffusion & Osmosis are both examples

of (u)... transport,

because the cell does not need to use

(v)... to make things

move.

As any shape gets larger, its

(w)... ratio gets

smaller. This is why all cells are small. A

large cell needs chemicals in proportion

to its x)...

However, it must get substances in

through its y)...,

the size of which is measured by its

z)... ...

The only way for living things to be

large, is to have aa)...

cells, NOT by having ab)...

cells.

WHEN COMPLETED,

WORKSHEETS BECOME SECTION SUMMARIES

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Multiple Choice

1. The man credited with the discovery of the cell nucleus was:

A.Robert Hooke.

B. Anton van Leeuwenhoek. C. Robert Brown.

D. Louise Pasteur.

2. The organelle least likely to be seen with a light microscope is:

A. Mitochondrion. B. Vacuole. C. Nucleus. D. Chloroplast.

3. The cell structure never found in an animal cell is:

A. cell membrane. B. cell wall.

C. endoplasmic reticulum. D. golgi body.

4. The function of the ribosomes can be described as:

A. storage of genetic information. B production of ATP.

C. packaging of substances for secretion. D. manufacture of proteins.

5. Starch, glycogen and cellulose are all: A. proteins, composed of amino acids. B. nucleic acids, related to DNA & RNA. C. sugars, of the carbohydrate group. D. polymers of glucose.

6. The diagram shows a cell surrounded by a solution which has a high concentration of large molecules.

You might expect:

A. solute molecules to diffuse into the cell. B. water to diffuse into the cell.

C. water to diffuse out of the cell.

D. solute molecules to diffuse out of the cell. 7. A brick was smashed into smaller pieces with a hammer. It would be true to say that all the brick pieces, when compared to the original brick, have:

A. larger total volume. B. larger SA/Vol ratio.

C. smaller total surface area.

8. A food substance, which may be a mixture of various organic chemicals, was tested with the following results:

Iodine solution gave a yellow, brown colour. Biuret reagent gave a purple colour.

Benedict’s reagent resulted in a pale blue colour. From these results you would conclude that the food contains:

A. protein, but no starch or sugar. B. starch, but no protein or sugar. C. sugar and protein, but no starch. D. sugar and starch, but no protein.

Longer Response Questions

Mark values given are suggestions only, and are to give you an idea of how detailed an answer is appropriate.

9. (3 marks)

Compare the light microscope to the electron microscope in terms of how each forms an image, the magnification, and the resolution of each.

10. (2 marks)

Using either the nucleus or mitochondrion as your example, discuss the way that the

structure of the organelle relates to its function.

11. (4 marks)

Using examples, discuss the difference between the “organic” & “inorganic” chemicals found in living cells.

12 (2 marks)

The cell membrane is described as being “semi-permeable”. Explain what this means.

13. (4 marks)

Compare the processes of diffusion and

osmosis, identifying what substances are involved and the direction of movement (compared to any “concentration gradient”)

14. (4 marks)

Explain why all living cells have to be very small in size.

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Photosynthesis in Plants

All plants make their own food from the simple,

low-energy raw materials water (H₂O) and

carbon dioxide (CO₂) using the energy of

sunlight, to make the high-energy sugar glucose

(C₆H₁₂O₆), with oxygen gas (O₂) as a by-product.

This brief summary equation is very deceptive. Photosynthesis actually occurs as a complex series of chemical steps inside the chloroplast. There are 2 main stages, which take place in different parts of the chloroplast, as summarized below.

Photosynthesis & Cellular Respiration

You will have noticed that these two vital processes, when written as summary equations, are exact opposites.

What is really happening is ENERGY FLOW through the food chains of an ecosystem. Photosynthesis captures the energy of light and stores it in a high energy food compound like glucose. Cellular respiration releases that stored energy in the form of ATP which can power all cellular and life activities... growing, moving, keeping warm etc.

As you learned in Topic 1, in all ecosystems there is a constant input and flow of energy via the food

chains, while the chemicals such as H₂O, O₂, and

CO₂simply get re-cycled over and over.

The Most Important Process on Earth

Photosynthesis makes all the food on Earth, for all the food chains. It also makes all the oxygen in the atmosphere for us animals to breathe.

For these two reasons, photosynthesis has to be the most important biological process on the planet.

3. NUTRITION IN PLANTS & ANIMALS

WATER + CARBON GLUCOSE + OXYGEN DIOXIDE 6H₂₂O + 6CO₂₂ C₆₆H₁₁₂₂O₆₆ + 6O₂₂ cchhlloorroopphhyyllll lliigghhtt ee_nneerrggyy lliigghhtt PPhhaassee 11 IInn tthhee ggrraannaa,,

cchhlloorroopphhyyllll aabbssoorrbbss lliigghhtt eenneerrggyy aanndd uusseess

iitt ttoo sspplliitt wwaatteerr iinnttoo hhyyddrrooggeenn aanndd

ooxxyyggeenn

PHOTOSYNTHESIS in the CHLOROPLAST PPhhaassee 22 IInn tthhee ssttrroommaa,, aa ccyyccllee ooff rreeaaccttiioonnss bbuuiillddss gglluuccoossee ffrroomm CCOO2 aanndd tthhee hhyyddrrooggeenn ffrroomm wwaatteerr LLiigghhtt eenneerrggyy MITOCHONDRIA - site of cellular respiration GLUCOSE + OXYGEN ATP ggrreeeenn ppiiggmmeenntt

iinn cchhlloorrooppllaassttss ooff ppllaanntt cceellllss

ttoo aaiirr hhiigghh-eenneerrggyy ssuuggaarr ((ffoooodd)) ffrroomm aaiirr ffrroomm ssooiill CHLOROPLAST - site of photosynthesis

Autotrophs & Heterotrophs

An autotroph is an organism that makes its own food. All plants are autotrophic, making their own food by photosynthesis.

Any organism that cannot make its own food must be a heterotroph. All animals are heterotrophic, and so are the fungi and most bacteria.

A heterotrophic animal eats plants or other animals which have eaten plants, and so on according to

the food chain involved. CARBON

DIOXIDE + WATER

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What Happens to Glucose in a Plant?

If photosynthesis only makes glucose, where do all the other biological chemicals in a plant come from? Glucose is a monosaccharide sugar, a member of the carbohydrate group. It is easy for a plant to convert glucose into other types of carbohydrate.

GLUCOSE molecules

jjooiinneedd iinn ppaaiirrss

jjooiinn eedd ii_{nn 11} 000000_’’ss ((ppoo_llyymm eerriiss_aattiioo nn)) O Otthheerr ssuuggaarrss,, ssuucchh aass ssuuccrroossee

CELLULOSE for building new

cell walls for storage of foodSTARCH In fact, plants convert glucose to STARCH so

rapidly that the chloroplasts in a plant leaf become packed with starch grains

when it is photosynthesising. THIS IS THE BASIS OF EXPERIMENTS

YOU MAY HAVE DONE

Soil minerals nniittrraattee,, ssuullffaattee eettcc

GLUCOSE _{Polymerisation}

AAmmiinnoo

aacciiddss PROTEIN cchheemmiiccaall

ccoonnvveerrssiioonn

Glucose can also be converted chemically into lipids... fats and oils, since they contain exactly the same chemical elements (carbon, hydrogen & oxygen only - CHO).

GLUCOSE LIPIDS (oils)

Making proteins and nucleic acids is more difficult, since these contain additional chemical elements, especially nitrogen, phosphorus and sulfur. This is where the “minerals” such as nitrate, phosphate and sulfate come in. Soil minerals are often called “plant nutrients”, and a gardener may say he/she is “feeding” the plants when applying fertilizer, but these minerals are NOT food.

They are the essential ingredients needed so plants can make proteins and DNA etc, from the real food... glucose.

Experiments with Photosynthesis

The classic experiment you have probably done, is to partly cover a leaf with light-proof aluminium foil, and then expose it to light for several days.

The aim is to prove that light is necessary for photosynthesis.

LLighht Iodine test shows lots of starch here No light, no starch

After several days, the leaf is decolourized (so the test can be seen more easily) and then tested with IODINE solution.

Why Iodine? It detects STARCH, not glucose. As explained above, the glucose produced by photosynthesis is immediately converted to starch. The iodine test is used because it is the

Sure enough, you probably found that any part of the leaf exposed to light turned black when soaked in iodine, while parts under the foil did not go black.

This proves that any part of a leaf allowed to photosynthesise will build up a store of starch from the glucose it makes. The first product of photosynthesis is glucose, but it is rapidly

Experimental Set-uup

Result

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Plants Absorb Water through special outgrowths on the roots called “root hairs”. Each root hair is part of one, very elongated cell. Root hairs help absorption of water by greatly increasing the surface area of the root in contact with the soil.

MICROSCOPIC VIEW NEAR A ROOT TIP

LONGITUDINAL TRANSVERSE SECTION SECTION XXYYLLEEMM TTUUBBEESS ROOT HAIRS O Ouuttggrroowwtthhss ffrroomm eeppiiddeerrmmiiss cceellllss

PPhhllooeemm ttuubbeess

EEppiiddeerrmmiiss llaayyeerr

The actual absorption of water is achieved by osmosis. The cell cytoplasm has a higher solute concentration than the water solution in the soil, so water diffuses into the cell through the cell membrane of the root hair cells.

Once absorbed into the root hair cells, water diffuses from cell to cell towards the central xylem tubes which carry the water (and dissolved minerals) upwards to the leaves. This upward flow is achieved by the plant constantly allowing water vapour to evaporate from each leaf (“Transpiration”). This creates a “suction” at the top of the xylem tube, rather like drinking through a straw.

Alongside the xylem tubes are the phloem tubes which carry food from the leaves to any part of the plant which cannot photosynthesize... especially down to the roots.

Together the xylem and phloem tubes form the “veins” in a plant. They not only carry substances around the plant, but are important as reinforcement and support structures.

Structure & Function... How Plants Get Water & Carbon Dioxide

In order to photosynthesise, plants must collect water and carbon dioxide. In a land plant, water is collected by the roots from the soil, and carbon dioxide is collected from the air into the leaves.

Both roots and leaves require special structures to gather these vital chemicals.

The Importance of Surface Area

It is generally true of many processes such as absorption and chemical reactions, that the greater the surface area, the faster the rate of the process.

You may have done a simple experiment similar to

this:-The more finely divided a solid is, the greater its surface area, so the powder has more surface area than the lumps.

This experiment demonstrates the principle that things happen faster when more surface area is available for reaction or absorption.

Same quantity of same strength acid Same quantity

of solid calcium carbonate on

each spoon

Lumps _Powder

Both lumps and powder react with acid in exactly the same way, but you would observe that the powder reacts

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The Structure of the Leaf

A plant leaf is a factory for photosynthesis. A typical leaf is built so that every part of its design is suited to the achievement of that one objective... making food. It is a classic case of Structure matches Function.

MICROSCOPIC CROSS SECTION THROUGH A LEAF SURFACE VIEW OF A STOMATE m maaggnniiffiieedd aanndd rroottaatteedd ttoo ssuurrffaaccee vviieeww The cuticle is a layer of clear,

waxy material. It allows light through, but is waterproof to

prevent excessive water loss. The epidermis

layer of cells is transparent like a window, to let light through to the cells underneath. The Palisade Layer of

cells are tightly packed in an orderly row immediately under the top

epidermis where there is maximum light. Each cell

contains many chloroplasts. This is the

“engine room” for photosynthesis.

The Spongy Layer has very loosely packed

cells, with lots of spaces around them.

This allows gases (CO₂

& O₂) and water to

easily move around by diffusion.

The lower leaf surface has many openings, called “stomates”. These allow:

• water to evaporate from the leaf (Transpiration). This ensures that water and minerals continue to be “sucked up” from the roots.

• CO₂to diffuse into the leaf for photosynthesis.

• O₂to diffuse out of the leaf into the air.

A magnified surface view of a stomate is shown.

Veins run throughout each leaf. The xylem tubes

bring water and minerals from the roots and release them into the spongy layer.

From there, some diffuses into the cells for photosynthesis, while the rest evaporates through the

stomates.

There are phloem tubes as well, which collect the food manufactured in the leaf cells and carry it away to

feed other parts of the plant, such as roots, stem

and flowers which might not be able to photosynthesise. Veins also act as reinforcing, helping to keep the flimsy leaf deployed to

catch maximum light. PPoorree

ooppeenniinngg A leaf is generally broad, flat and

thin. This gives it maximum surface area for absorbing light and carbon dioxide from the air.

A leaf is thin enough that light penetrates to reach each layer of

cells within, for maximum photosynthesis.

The “veins” contain xylem tubes for carrying water and minerals up from

the roots, and phloem tubes for carrying manufactured food away.

Being specially reinforced with tough “lignin”, the veins also support the flimsy leaf, and keep it

in shape and positioned to catch maximum light.

Each stomate pore is an opening formed between two special “guard cells”. These cells can change shape

to open the pore, or close it up to minimize water loss in dry conditions. The guard cells change

shape by using osmosis to either pump-up full of water (pore open), or

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Nutrition in Animals

Animals are Heterotrophs.

They must eat energy-rich food made by other organisms, either plants or other animals. The food an animal eats is composed largely of

complex carbohydrates, proteins and fats which must be digested before being absorbed into the body and used by the cells.

Digestion involves chemically breaking large molecules down into smaller units which can be carried around the body and transported across cell membranes.

EENNZZYYMMEE Starch molecule Sugar molecules Protein molecule

EENNZZYYMMEE

Amino acid molecules

HUMAN DIGESTIVE SYSTEM

Chewing the food begins the digestion process. Chewing breaks food into smaller pieces with greater

surface area, so digestive enzymes can attack it faster.

Salivary Glands.

An enzyme in saliva begins digesting starch.

Liver receives and processes digested nutrients after they are absorbed into

blood stream.

Gall bladder adds bile to dissolve fats so enzymes

can digest them. Small Intestine completes digestion with a

cocktail of enzymes, then absorbs nutrients into the

blood stream. Inside, it has many folds or “villi” which increase surface

area for absorption.

Caecum & Appendix have no special functions

in humans

Oesophagus

carries food to the stomach.

Stomach

churns food with acid. Enzymes digest proteins in food

Large Intestine

absorbs water, vitamins & minerals into blood stream. Rectum stores undigested wastes (faeces) for later elimination.

Pancreas

adds a cocktail of enzymes to futher digest food

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Digestion in Herbivores

Plant-eaters face a problem... a lot of plant material has a low nutrient value and contains a lot of fibrous matter which is difficult to digest. The fibre is mostly the plant cell walls, made of cellulose... a polymer of glucose, but animals lack the necessary digestive enzymes to break the cellulose down. Herbivores usually

have:-• flat, grinding teeth to chew the food thoroughly to increase the surface area exposed to enzymes. • relatively long intestines and caecum, for more

surface area and longer time available for digestion.

• bacteria living in their gut which have enzymes to digest cellulose.

This is an example of “mutualism”.

LLoonngg LLaarrggee IInntteessttiinnee H Huuggee CCaaeeccuumm SSttoommaacchh LLoonngg SSmmaallll IInntteessttiinnee GGrriinnddiinngg tteeeetthh

Digestion in Carnivores

Flesh eaters don’t need such huge digestive systems. Their food is much more concentrated in its nutritional value, and relatively easy to digest.

Carnivores usually have:-• sharp, tearing teeth to cut flesh into chunks for swallowing... chewing is not so important.

• relatively short intestines.

• a highly elastic stomach, which allows them to swallow a large meal. The stomach acid and enzymes are vital for digesting their high protein meat diet.

Different Animals Have Different Systems

The digestive systems of different animals are often quite similar, but certainly not identical. Once again, the principle of “structure matches function” can be noticed.

SShhoorrtteerr iinntteessttiinneess SSttoommaacchh m moorree iimmppoorrttaanntt

Digestion in a Nectar Feeder

Some animals eat a diet that requires very little digestion at all. Many birds (eg honey-eaters, humming birds) and insects (eg butterflies)

feed largely on the sugary nectar of flowers.

Sugar does not require any digestion at all, so their digestive system can be very short and simple.

A short-lived butterfly only needs nectar for the energy its sugar supplies, but a bird needs more nutrients. Most eat the plant pollen which is rich in

protein and oil. Therefore, their short little digestive system does need to do some work, apart from simply absorbing sugar.

Nectar & Pollen feeding lorikeet

TTeeaarriinngg tteeeetthh

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Worksheet 4

Nutrition in Plants

Fill in the blanks.

(a)... (e.g. plants) are

organisms that can make their own food,

while (b)... (such as

animals) cannot.

The process of photosynthesis can be

summarized as

(c)... + (d)...

(e)... + (f)...

Photosynthesis occurs in the

(g)... (organelle) in plant

cells. The green pigment (h)...

absorbs (i)... energy for the

process. This energy is stored as

chemical energy in the

(j)... molecules produced.

Thousands of glucose molecules can be

joined together by the process of

(k)... to form (l)...

(used for storage) or cellulose which is

used to build (m)...

Glucose can also be chemically converted

into (n)... To convert

sugar to amino acids, the plant needs a

supply of (o)...

Amino acids can then be joined

together to form (p)...

The structures mainly responsible for

absorbing water into a plant are the

(q)... which are

outgrowths of root cells and greatly

increase the (r)...

of the roots. Water is absorbed by the

process of (s)...

then transported up to the leaves

through (t)... tubes.

In a leaf, there are many examples of

“structure matching function”, such as:

• The shape of the leaf gives maximum

surface area for (u)...

• The (v)...

layer of cells, packed together & full of

chloroplasts for maximum photosynthesis.

• The “spongy layer” of loosely packed

cells to allow (w)...

• The (x)... which

can open and close and allow water to

evaporate (called (y)...)

and to let the gas (z)...

in for photosynthesis.

Worksheet 5

Nutrition in Animals

Fill in the blanks

Animals have to digest the food they

eat. This is carried out by digestive

(a)... which, for example,

break starch into (b)... and

proteins into (c)...

There are 4 organs in the mammal

digestive system that produce digestive

enzymes. Name them all.

(d)..., ...

... and ...

Digestion begins with chewing food

which increases the (e)...

of the food, so enzymes can attack it

faster.

Digested nutrients are absorbed into the

blood stream from the (f)...,

then carried in the blood to the

(g)... for processing.

Herbivorous animals usually have:

• (h)... teeth to chew thoroughly

• relatively (i)... intestines and caecum

• mutualistic (j)... living in their

gut to help them digest (k)...

which is a major part of their diet.

Compared to them, carnivores usually

have (l)... teeth and

relatively (m)... intestines

Nectar feeders, such as (n)...

have digestive systems which are very

(o)... and ...

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Multiple Choice

1. The chemical raw materials needed for photosynthesis are:

A. glucose and oxygen. B. water and carbon dioxide. C. carbon dioxide and oxygen. D. water and glucose.

2. The chemical “ATP” is best described as: A. the carrier of genetic information.

B. the product of cellular respiration. C. the absorber of light for photosynthesis. D. a waste product from the mitochondria. The following sketch shows a cross-section through a leaf. Use the diagram for Q. 3 & 4

3. A structural feature which helps the

functioning of the leaf is that the cells at “P”: A. are transparent

B. are loosely packed

C. contain many chloroplasts D. open up to let gases in/out 4. The “guard cells” are labeled

A. Q B. R C. S D. T

5. Soil minerals such as nitrates, phosphates and sulfates are essential to a plant for which purpose? A. To provide energy.

B. To make starch from glucose.

C. As raw materials for photosynthesis. D. To make proteins from glucose.

6. In a mammalian digestive system, the main chemical digestion in the stomach involves the breakdown of:

A. starch. B. protein. C. lipids. D. sugars.

7. An animal with large, flat, grinding teeth and a very large caecum (a blind “pocket” of the intestine) probably eats mainly:

A. nectar, pollen and flowers. B. the flesh of other animals. C. plant leaves and grass.

Longer Response Questions

Mark values given are suggestions only, and are to give you an idea of how detailed an answer is appropriate. Answer in the spaces provided. 8. (2 marks)

Differentiate between “autotrophs” & “heterotrophs”, including examples in your answer.

9. (5 marks)

a) Summarize the process of photosynthesis by a word equation, including the energy source.

b) Give two reasons why photosynthesis can be considered the most important biological process on Earth.

10. ( 5 marks)

In experiments on photosynthesis, the presence of starch in leaves is often taken as proof that photosynthesis has taken place.

a) Explain why it is starch, not glucose, that the leaves are tested for.

b) Outline the method of testing for starch in a leaf, including any preliminary treatment(s).

11. (4 marks)

Discuss the relationship between structure and function shown by the leaf cell layers known as the “palisade layer” & the “spongy layer”.

12. (3 marks)

Briefly outline how the length and complexity of an animal’s digestive system is related to its diet.

Refer to 3 different types of diets in your answer.

Worksheet 6 Practice Questions (Section 3)

P Q R

S

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Organisms Need What Cells Need

Every living cell, plant or animal, has certain

requirements:-A single-celled organism exchanges these chemicals with the environment directly through its cell membrane. However, in all multicellular organisms most of the cells are located deep within the body. There have to be body systems

to:-• absorb nutrients, water and oxygen • excrete wastes

• transport all these chemicals between the cells and the environment.

In animals the body systems involved are: Digestive system absorbs nutrients and water. Respiratory system (e.g. lungs) exchanges gases, absorbing oxygen, and excreting carbon dioxide. Excretory system (kidneys) removes other wastes such as urea.

Circulatory system (blood, heart, veins etc) transports all these things around the body. Plants also have systems for exchanging gases, and for transporting substances around their bodies.

Requirements for Gas Exchange

Plant or animal, large or small, all organisms need to exchange gases with their environment. Efficient gas exchange

requires:-• a large surface area

in contact with the environment. • a moist gas exchange membrane

because the gases must dissolve in water before passing through the membrane by diffusion. • close contact with the blood supply

(or other transport system) to carry gases between cells and the gas exchange organs.

Gas Exchange in Animals

There are many ways that animals carry out gas exchange. This section will compare four different systems... mammal, frog, fish and insect.

Lungs in a Mammal

Using the human as a typical example:

The lung is not just a hollow space like a balloon.

If it was, the surface area for

gas exchange would be about the size of this page. By dividing into millions of alveoli, the total surface area inside your lungs is about the same size as a tennis court!

The inside surface is always moist, for gases to dissolve and diffuse, and each alveolus is in intimate contact with a blood capillary to transport the gases to and from the body cells.

The requirements for efficient gas

exchange have been met.

4. GAS EXCHANGE & INTERNAL TRANSPORT

FOOD in WATER in OXYGEN in

WASTE PRODUCTS such as CO₂₂must be excreted

AAIIRR fflloowwss iinn aanndd oouutt

Blood capillary BBlloooodd ffllooww O₂₂ CO₂₂ Bronchiole Trachea (Windpipe) Each bronchus sub-ddivides into Bronchioles Lungs are not hollow, but sponge-llike Bronchi (sing: bronchus) carry air to each lung EEaacchh bbrroonncchhiioollee

eennddss iinn aa cclluusstteerr ooff ttiinnyy aaiirr ssaaccss... tthheeAlveoli

Each Alveolus has a wall just 1 cell thick, and the

internal surface is kept moist

HUMAN RESPIRATORY