Chapter 8 Revised.pptx

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REVIEW OF CELLS

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INTRODUCTION TO CELL

TRANSPORT

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• Diffusion is the movement of particles from

an area of higher concentration to an area of lower concentration.

Osmosis: Diffusion of Water

• In a cell, water always moves to reach an

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• The diffusion of water across a selectively

permeable membrane is called osmosis.

Osmosis: Diffusion of Water

• Regulating the water flow through the

plasma membrane is an important factor in

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• Unequal

distribution of particles,

called a concentration gradient, is one factor that controls osmosis.

What controls osmosis?

Before

Osmosis OsmosisAfter

Water molecule Sugar molecule

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Cells in an isotonic solution

• In an isotonic

solution, the

concentration of

dissolved substances in the solution is the same as the

concentration of

dissolved substances inside the cell.

H₂O

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Cells in an isotonic solution

• In an isotonic

solution, water molecules move into and out of the cell at the same rate, and cells retain their normal shape.

H₂O

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Cells in an isotonic solution

• A plant cell

has its normal

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Cells in a hypotonic solution

• In a hypotonic

solution, water enters a cell by osmosis, causing the cell to swell.

H2O

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Cells in a hypotonic solution

• Plant cells swell

beyond their normal size as

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Cells in a hypertonic solution

• In a hypertonic

solution, water leaves a cell by osmosis, causing the cell to shrink.

H2O H₂O

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Cells in a hypertonic solution

• Plant cells lose

pressure as the plasma

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Passive Transport

• When a cell uses no energy to move particles

across a membrane passive transport occurs.

Concentration gradient

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Passive Transport by proteins

• Passive transport of materials across the

membrane using transport proteins is called

facilitated diffusion.

Plasma membrane

Channel proteins

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Passive Transport by proteins

• Some transport proteins, called channel

proteins, form channels that allow specific molecules to flow through.

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Passive transport by proteins

• The movement is with the concentration

gradient, and requires no energy input from the cell.

Concentration gradient Plasma

membrane

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Passive transport by proteins

• Carrier proteins change shape to allow a

substance to pass through the plasma membrane.

Concentration gradient Plasma

membrane

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Passive transport by proteins

• In facilitated diffusion by carrier protein, the

movement is with the concentration gradient and requires no energy input from the cell.

Step 1 Step 2 Carrier proteins

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Active Transport

• Movement of materials through a membrane

against a concentration gradient is called

active transport and requires energy from the cell.

Plasma

membrane Concentration gradient

Carrier proteins

Cellular energy

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How active transport occurs

• In active transport, a transport protein called

a carrier protein first binds with a particle of the substance to be transported.

Plasma

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How active transport occurs

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How active transport occurs

• Each type of carrier protein has a shape that

fits a specific molecule or ion.

Plasma

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How active transport occurs

• When the proper molecule binds with the

protein, chemical energy allows the cell to change the shape of the carrier protein so that the particle to be moved is released on the other side of the membrane.

Step 1 Step 2

Plasma

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How active transport occurs

• Once the particle is released, the protein’s

original shape is restored.

Step 1 Step 2

Plasma

• Active transport allows particle movement

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How active transport occurs

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Transport of Large Particles

• Endocytosis is a process by which a cell

surrounds and takes in material from its environment.

Endocytosis Exocytosis

Digestion

Nucleus

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Transport of Large Particles

• The material is engulfed and enclosed by a

portion of the cell’s plasma membrane.

Exocytosis

Digestion

Nucleus

Wastes

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Transport of Large Particles

• The resulting vacuole with its contents

moves to the inside of the cell.

Exocytosis

Digestion

Nucleus

Wastes

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Transport of Large Particles

• Exocytosis is the expulsion or secretion of

materials from a cell.

Digestion

Nucleus

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Transport of Large Particles

• Endocytosis and exocytosis both move

masses of material and both require energy.

Digestion

Nucleus

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Question 1

B. endocytosis

A.

active transport

The diffusion of water across a selectively permeable membrane is called __________. Water molecule Sugar molecule Selectively permeable membrane

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Question 1

D. osmosis C. exocytosis The diffusion of water across a selectively permeable membrane is called __________. Water molecule Sugar molecule Selectively permeable membrane

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The answer is D, osmosis. Regulating the water flow through the plasma

membrane is an important factor in maintaining homeostasis within the cell.

Selectively permeable membrane

Before osmosis After osmosis

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What is the expected result of having an animal cell in a hypertonic solution?

Question 2

D. The cell retains its normal shape. C. The cell swells up.

A. The cell shrivels up.

B. The plasma membrane shrinks away from

the cell wall.

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The answer is A. In a hypertonic solution, cells experience osmosis of water out of the cell.

Animal cells shrivel because of decreased pressure in the cells.

H2O

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A grocer mists the celery display with water to keep it looking fresh. What type of solution is the celery now in?

Question 3

D. exotonic C. hypertonic B. hypotonic A. isotonic

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The answer is B. Plant cells contain a rigid cell wall and do not burst even in a hypotonic

solution.

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Transport of materials across the plasma

membrane that does not require energy from the cell but does use transport proteins is called

__________.

Question 4

B. simple diffusion A. osmosis Plasma

CA: Biology/Life Sciences 1a

C. facilitated diffusion D. active

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The answer is C. Facilitated diffusion is a type of passive transport and requires no energy

from the cell.

Plasma

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Cell Size Limitations

• The cells that make up a multicellular

organism come in a wide variety of sizes and shapes.

• Considering this wide range of cells sizes,

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Diffusion limits cell size

• Although diffusion is a fast and efficient

process over short distances, it becomes slow and inefficient as the distances become

larger.

• Because of the slow rate of diffusion,

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DNA limits cell size

• The cell cannot survive unless there is

enough DNA to support the protein needs of the cell.

• In many large cells, more than one nucleus

is present.

• Large amounts of DNA in many nuclei

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Surface area-to-volume ratio

• As a cell’s size increases, its volume

increases much faster than its surface area. Surface area = 6 mm2

Volume = 8 mm3

Surface area = 24 mm2

Volume = 8 mm3

1 mm 1 mm

1 mm

2 mm 2 mm

2 mm

4 mm _{4 mm}

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Volume = 8 mm3

1 mm 1 mm

1 mm

2 mm 2 mm

2 mm

4 mm _{4 mm}

4 mm

• If cell size doubled, the cell would require

eight times more nutrients and would have eight times more waste to excrete.

Surface area-to-volume ratio

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• The surface area, however, would increase by

a factor of only four.

Surface area-to-volume ratio

Volume = 8 mm3

1 mm 1 mm

1 mm

2 mm 2 mm

2 mm

4 mm _{4 mm}

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Surface area-to-volume ratio

Volume = 8 mm3

1 mm 1 mm

1 mm

2 mm 2 mm

2 mm

4 mm _{4 mm}

4 mm

• The cell would either starve to death or be

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Cell Reproduction

• Cell division is the process by which new

cells are produced from one cell.

• Cell division results in two cells that are

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The discovery of chromosomes

• Structures, which contain DNA and become

darkly colored when stained, are called

chromosomes.

• Chromosomes are the carriers of the genetic

material that is copied and passed from generation to generation of cells.

• Accurate transmission of chromosomes

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The structure of eukaryotic chromosomes

Centromere

Chromosome Sister

chromatids

Supercoil within chromosome

Continued coiling within supercoil

Histone H1

Nucleosome

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The Cell Cycle

• The cell cycle is the sequence of growth and

division of a cell.

• The majority of a

cell’s life is spent in the growth

period known as

interphase.

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The Cell Cycle

• Following interphase, a cell enters its period

of nuclear division called mitosis.

• Following

mitosis, the cytoplasm divides,

separating the two daughter cells.

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Interphase: A Busy Time

• Interphase, the busiest phase of the cell

cycle, is divided into three parts.

DNA synthesis

and replication _{Centrioles replicate;} cell prepares for

division Rapid

growth and

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Interphase: A Busy Time

• During the first part, the cell grows and

protein production is high.

Rapid growth

and metabolic

activity

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Interphase: A Busy Time

• In the next part of interphase, the cell copies

its chromosomes.

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Interphase: A Busy Time

• After the chromosomes have been

duplicated, the cell enters another shorter growth period in which mitochondria and other organelles are manufactured and cell parts needed for cell division are assembled.

Centrioles replicate; cell prepares for

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The Phases of Mitosis

• The four phases of mitosis are prophase,

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Prophase: The first phase of mitosis

• During prophase, the chromatin coils to form

visible chromosomes.

Spindle fibers Disappearing nuclear envelope

Doubled

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Prophase: The first phase of mitosis

• The two halves of the doubled structure are

called sister chromatids.

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Prophase: The first phase of mitosis

• Sister chromatids are held together by a

structure called a centromere, which plays

a role in chromosome movement during mitosis.

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Metaphase: The second stage of mitosis

• During metaphase, the chromosomes move

to the equator of the spindle.

Centromere

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Anaphase: The third phase of mitosis

• During anaphase, the centromeres split and

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Telophase: The fourth phase of mitosis

• During telophase, two distinct daughter cells

are formed. The cells separate as the cell cycle proceeds into the next interphase. Nuclear

envelope reappears

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Cytokinesis

• Following telophase, the cell’s cytoplasm

divides in a process called cytokinesis.

• Cytokinesis differs between plants and

animals.

• Toward the end of telophase in animal cells,

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Cytokinesis

• Plant cells have a rigid cell wall, so the

plasma membrane does not pinch in.

• A structure known as the cell plate is laid

down across the cell’s equator.

• A cell membrane forms around each cell,

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Results of Mitosis

• When mitosis is complete, unicellular

organisms remain as single cells.

• In multicellular organisms, cell growth and

reproduction result in groups of cells that

work together as tissue to perform a specific

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Results of Mitosis

• Tissues organize in various combinations to

form organs that perform more complex

roles within the organism.

• Multiple organs that work together form an

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The stringy structures in the cell nucleus that contain DNA are __________.

Question 1

D. chlorophylls C. genes

B. chromosomes A. centromeres

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The answer is B. Chromosomes are the carriers of the genetic material of the cell. A gene is a segment of DNA that controls the production of a protein.

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Look at the diagram and identify the stage of mitosis that is depicted.

Question 2

D. telophase C. anaphase B. metaphase

A. prophase

Centromere

Sister

chromatids

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The answer is B. Metaphase is the short second phase of mitosis, during which the

chromosomes begin to line up on the equator of the spindle.

Centromere

Sister

chromatids

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What is the process by which a cell's cytoplasm divides?

Question 3

D. mitosis C. meiosis

B. telekinesis A. cytokinesis

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The answer is A. Cytokinesis follows telophase and allows the two new cells to separate.

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In multicellular organisms, groups of cells that work together to perform a specific function

are called __________.

Question 4

D. cell cycles C. tissues

B. organs

A. organ systems

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The answer is C. Tissues organize to form

organs, which work with other organs to form organ systems.

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Section Objectives

• Describe the role of enzymes in the

regulation of the cell cycle.

• Distinguish between the events of a normal

cell cycle and the abnormal events that result in cancer.

• Identify ways to potentially reduce the risk

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Normal Control of the Cell Cycle

• The cell cycle is controlled by proteins called

cyclins and a set of enzymes that attach to the cyclin and become activated.

• Occasionally, cells lose control of the cell

cycle.

Proteins and enzymes control the

cell cycle

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Normal Control of the Cell Cycle

• Cancer is a malignant growth resulting from

uncontrolled cell division.

• This uncontrolled dividing of cells can result

from the failure to produce certain enzymes, the overproduction of enzymes, or the

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Normal Control of the Cell Cycle

• Enzyme production is directed by genes

located on the chromosomes.

• A gene is a segment of DNA that

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Cancer: A mistake in the Cell Cycle

• Currently, scientists consider cancer to be a

result of changes in one or more of the genes that produce substances that are involved in controlling the cell cycle.

• Cancerous cells form masses of tissue called

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Cancer: A mistake in the Cell Cycle

• In later stages, cancer cells enter the

circulatory system and spread throughout the body, a process called metastasis, forming

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The causes of cancer

• The causes of cancer are difficult to pinpoint

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The causes of cancer

• Environmental

factors, such as

cigarette smoke, air and water pollution, and exposure to

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The causes of cancer

• Cancer may also be caused by viral

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Cancer prevention

• Physicians and dietary experts agree that diets

low in fat and high in fiber content can reduce the risk of many kinds of cancer.

• Vitamins and minerals may also help prevent

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Cancer prevention

• In addition to

diet, other healthy choices such as

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A(n) __________ is a segment of DNA that controls the production of a protein.

Question 2

D. chromosome C. enzyme

B. cyclin A. gene

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The answer is A. Genes control the production of proteins. Scientists think that cancer results from changes in one or more of the genes that produce substances controlling the cell cycle.

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Which of the following is thought to reduce the risk of developing cancer?

Question 3

D. decrease dietary minerals C. decrease dietary fiber

B. increase dietary fiber A. increase dietary fat

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The answer is B. Health professionals believe that diets low in fat and high in fiber content can reduce the risk of many types of cancer.

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RECAP MITOSIS

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