Edexcel GCE Biology Unit 2 Exam Revision Notes

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Biology Unit 2 Exam Revision Notes

The Five Kingdoms

Prokaryotes E.g. Bacteria  no nucleus

 loop of naked DNA

 DNA not arranged in linear chromosomes

 no membrane-bound organelles

 smaller ribosome’s than other groups

 carry out respiration on mesosome’s (special membrane systems), not mitochondria

 smaller cells than eukaryotes

 parasitic (some cause disease)

Protoctista E.g. Algae  eukaryotes

 mostly single-celled

 autotrophic/heterotrophic nutrition

 do not belong to any other kingdoms

Fungi E.g. Moulds, yeast, mushrooms  multi-cellular eukaryotes

 heterotrophic (plants and animals) and saptrophic (absorb food from the dead)

Plantae E.g. Mosses, Ferns, flowering plants  multi-cellular eukaryotes

 cells surrounded by cellulose cell wall

 produce multi-cellular embryos from fertilised eggs

 autotrophic (make their own food) nutrition

Animalia E.g. molluscs, insects, fish, reptiles, birds, mammals  multi-cellular eukaryotes

 heterotrophic (plants and animals) nutrition

 fertilised eggs that develop

 usually able to move around

Binomial Naming System: Genus then Species : minimises confusion – all scientists, in all

countries, call a species by the same name.

Evolution of Classification


Only use to be based on observations to place organisms into groups, but physical features may not show how closely related organisms are. Now, it’s based on observations and evidence. The more similar, the more closely related, the other evidence used:

Molecular: similarities in DNA etc. e.g. Chimps and Humans share 94% of DNA.

Embryological: early stages of development.

Anatomical: structure/function of body parts.

Behavioural: similarities in behaviour and social organisation. New Scientific Data can lead to new taxonomic groupings:

 New data about any of characteristics can influence the way species are classified  New data has to be evaluated by other scientists to check if it’s actually there. If all

scientists agree it can lead to a new organism being reclassified or leads to changes in the classification system structure

Taxonomic Hierarchy Domain Kingdom Phylum Class Order Family Genus Species


3 Domains

Bacteria have:

 different cell membrane structure

 different internal structure of the flagella

 different enzymes (RNA polymerase) for building RNA

 no proteins bound to their genetic material

 different mechanisms for DNA replication and building RNA

Archaea and Eucarya share:

 similar enzymes (RNA polymerase) for building RNA

 similar mechanisms for DNA replication and building DNA

 production of some proteins that bind to their DNA

Bacteria: Prokaryote kingdom e.g. methanogens

Archaea: Prokaryote kingdom e.g. all other bacteria (apart from methanogens)

Eucarya:Organisms from the other four kingdoms (not prokaryote), Eukaryotic e.g. plants/ animals/ fungi

Three domains vs Five Kingdoms

A new, three domain classification system has been proposed (1960) based on new data. The new data came from molecular phylogeny (study of the evolutionary history of groups of

organisms, telling us which species are related to which and how closely related they are).

Molecular phylogeny looks at molecules (DNA and proteins) to see how closely related organisms are, e.g. more closely related organisms have more similar molecules

This new system classifies organisms in a different way:

 In the older, five kingdom system of classification, all organisms are placed into one of five kingdoms

 In the new, three domain system all organisms are placed into one of three domains – large super -kingdoms that are above the kingdoms in the taxonomic hierarchy

 Organisms that were in the kingdom Prokaryote (unicellular organisms without a nucleus) are separated into two domains – the Archaea and Bacteria. Organisms from the other four kingdoms (organisms with cells that contain a nucleus) are placed in the third domain – Eukarya

 The Prokaryote were reclassified into two domains because molecular phylogeny suggested that Archaea and bacteria are more distantly related than originally thought. Why classify?

 for convenience

 make study of living things more manageable  easier to identify organisms

 help see relationships between species

Taxonomic Hierarchy: placing organisms into a series of smaller and smaller groups (taxa),

where all members share one or more features or homologies.

Taxonomy: the study of the differences between species eg: morphology, nutrition which are used

place organisms in groups. It involves naming organisms and organising them into groups based on their similarities and differences. This makes it easier for scientists to identify them and to study them.

Phylogeny: History of the evolution from a shared ancestor, tells us who's related to whom and



 a group of organisms with similar morphology (looks the similar), physiology (internally similar, chemically) and behaviour (how they act)

 which can interbreed to produce fertile offspring

 and which are reproductively isolated from other species

Habitat: a place with a distinct set of conditions where an organism lives Population: a group of individuals of the same species found in an area

Community: the various populations of different species that share an ecosystem/ habitat


 the precise role of an organism in its environment  the sum total of all the organisms' interactions A niche can only be occupied by one species.

Gene Pool: the sum total of all alleles of all genes within a population

Adaptation: features which enable an organism to survive and reproduce and being specialised to

suit an environment in which the organism lives

Behavioural Adaptations: any actions by organisms, which help them to survive and reproduce. Physiological Adaptations: features of the internal workings of an organism, which help them to

survive and reproduce.

Anatomical Adaptations: physical structural features of an organism's body, which help them to

survive and reproduce

Co-adaptation: when two organisms become dependent of each other and more and more

closely adapted

Natural Selection: organisms change over time as they adapt to their changing environment

Natural Selection: Observation: more offspring produced than can survive Struggle for existence:

 competition for survival between members of the same species for resources such as food  limited resources between too many organisms

 population size is limited by environment

Observation: huge amount of inherited variation between species Survival of the Fittest:

 organisms best adapted to the environment are more likely to obtain resources (e.g. food)  and so more likely to survive and reproduce

A mutation in a gene may result in a change in the physical appearance of an organism, in its physiology or even in its pattern of behaviour. If this change is advantageous, the frequency of those alleles within the population will increase. The changing environment also leads to many species having to adapt to the changes in the climate or different animals that have migrated to the area that could be potential predators.

Evolution: a change in the frequency of alleles over time

Evolution occurs when:

 Variation exists within a species through random genetic mutations, which form new alleles  Meiosis mixes up existing allele combinations


 Change in environment causes a change in the selection pressure  Which causes a change in allele success

 Some alleles are favourable and some are harmful

 Organisms with favourable alleles survive and reproduce, forming fertile offspring  Those who have the harmful allele do not

 Inheritance of the favourable allele occurs, increasing the frequency of that allele in the next generation

Biodiversity: is the variety of living organisms in an area

Species Diversity: number of different species and abundance of each species in an area Genetic Diversity: variety of alleles within a species or population

Ecological Diversity: variety between different habitats Endemism:

— Species is unique to a single place

— Isn't naturally found anywhere-else in the world E.g. the giant tortoise is endemic to the Galapagos Islands Measure Genetic Diversity within a species:

Find the number of different alleles in the gene pool by DNA Sequencing.

This determine the bases in a DNA segment and determining the alleles present Measure species biodiversity:

1. Species Richness: count the number of different types of species in a given habitat. The more types of species, the greater the species richness. But,species richness gives no indication of the abundance of each species

2. Species Evenness: count the number of different types of species in a given habitat and the number of individuals of each species. Then use a biodiversity index (e.g. Simpson’s Index of Diversity) to calculate the species diversity. This takes into account the number and abundance of each species.

A sample of the population is taken and estimates are then made about the whole habitat based on the sample. Sampling involves:

1. Choose a specific area to sample – a small area within a habitat being studied

2. To avoid bias, the sample should be random – use a random number generator to select coordinates (maybe use a quadrat)

3. Count the number of individuals of each species in the sample area: plants- quadrat, flying insects - sweepnet (net on a pole), ground insects - pitfall trap (small pit that insects can’t get out of), aquatic animals - net

4. Repeat the whole process taking as many samples as possible. This gives a better indication of the whole habitat

5. Use the results to estimate the total number of individuals or the total number of different species (species richness) in the habitat being studied

When sampling different habitats and comparing them, always use the same sampling technique. Sources of variation in genetic diversity:

 Gene mutations

 Independent Assortment  Crossing Over

 Mate Selection  Random Fertilisation

Genetic Diversity can be measured by:  DNA Analysis: DNA base

sequence used to identify different alleles

 Heterozygosity Index: the proportion of genes present in heterozygous form.


Organelles in plant cells (Eukaryotic Cell):

(Plus: Nucleus, rER, sER, ribosome’s, Golgi apparatus and cytoplasm)


 has a double membrane  storage of starch grains


 regions of thin cell wall

 allows transport of substances between cells


 channels in cell wall that link adjacent cells together  allows transport and communication between cells

Middle Lamella:

 is an adhesive sticking adjacent plant cells together  gives plant stability

 contains pectin’s


 contains cell sap (water, enzymes, minerals and waste products)  keeps cell turgid (stops plant wilting)

 involved in the breakdown and isolation of unwanted chemicals in cell  has a tonoplast (membrane)- controls what enters and leaves the vacuole

Cell Wall:

 made of Cellulose  supports plant cells


 double membrane

 membrane stacked up to form grana

 photosynthesis takes place here (in grana or stroma-a thick fluid)


 membrane

 store starch grains

 convert starch to glucose for release

Organelles in animal cells (Eukaryotic Cell):

(Plus: Nucleus, rER, sER, ribosome’s, Golgi apparatus and cytoplasm)


 hollow cylinders containing microtubules  separation of chromosomes in cell division


 small fluid filled sac in cytoplasm surrounded by a membrane  transports substances in and out of the cell


 shape: round

 membrane containing digestive enzymes (digest invading cells or break down worn out components of the cell



 oval shaped

 double membrane (inner forms cristae)  matrix (contains enzymes for respiration)  site of aerobic respiration- ATP is produced

Organelles in both plants and animals (Eukaryotic Cell):


 nuclear envelope ( double membrane) with pores

 contains chromatin (DNA) and often nucleolus (makes ribosome’s)


 small organelle

 float free or attached to rough endoplasmic reticulum (rER)  site were proteins are made


 covered in ribosome’s  processes proteins


 system of membranes enclosing a fluid filled space  synthesises and processes lipids and steroids

Golgi Apparatus:

 group of fluid filled flattened sacs  vesicles at edge

 processes and packages lipids and proteins  Makes lysosomes

Prokaryotic Cells: E.g. Blue Green Algae

Ribosome (smaller than eukaryotic ones), Cytoplasm, Cell surface membrane Cell Wall:

 made of peptidoglycan (polysaccharide protein)


 Small circle of DNA


 infolding of a cell surface membrane  site of respiration

Slime Capsule: (some)

 prevents dehydration  protection

Flagellum: (some)

 propel the cell (swim)

Differences in plant and animal cells:

 plant cell has a rigid wall, and animal does not  plant cells contain chloroplasts, animals don’t


Prokaryotic Eukaryotic

Size Smaller: 0.5-5 m Larger: 5-200m

DNA Circular

Free in cytoplasm NO NUCLEUS

Linear In nucleus

Organelles No membrane bound

organelles No nuclei

Small ribosome’s

Membrane bound organelles Nucleus

Larger ribosome’s

Cell Wall Always present Not always present

— Cellulose cell wall in Plants — Chitin cell wall in Fungi

Cellulose is a strong structural support because:

 large number of hydrogen bonds forming bundles called Microfibrils in layers

 within matrix of hemicelluloses and pectin’s (glue that holds Microfibrils together)

A turgid cell is one that is completely full with its cell contents pressing out on the cell wall. If it loses its turgidity, the plant wilts.

Parenchyma: type of plant tissue found throughout the plant. Fill space in the stem.

Vascular bundle: contains xylem vessels and phloem (transport of products of photosynthesis)

Xylem vessels  Phloem  Sclerenchyma fibres There are 3 main types of tissue found in plants:

 The vascular tissue is found at the centre of the stem. Each vascular bundle contains xylem vessels and phloem sieve tubes, on the outside of the bundle are Sclerenchyma fibres.

Starch: o Alpha Glucose

o Branched amylopectin (1, 4 and 1,6 glycosidic bonds) and unbranched amylose (1, 4 glycosidic bonds) o Chains with branches so spiral

(helical coiled)

o Energy storage in plants

Cellulose: o Beta Glucose

o Unbranched

o Long straight chains

o Strong structural support for plants o Microfibrils

Sclerenchyma Fibres:  Bundles of dead cells

 Hollow Lumen  Columns

 Provide support

 Walls thickened with lignin (strength, waterproof) and contain more cellulose  Short structures with ends closed  No pits

Xylem Vessels:  Bundles of dead cells

 Hollow Lumen  Columns

 Transport water + minerals up the plant and provide support

 Walls thickened with lignin (strength, waterproof)  Long cylinders with no end walls

 Pits to allow transport of water + ions out of xylem


 The ground tissue is found surrounding the vascular tissue in the middle section of a cross-section of a stem (Parenchyma tissue)

 The (dermal tissue) epidermis is on the outer layer of the stem. Xylem vessels for transport:

Xylem vessels are made up of large cells with thick cell walls. They form a column of cells acting as tubes for the transport of water and mineral ions.

The plant produces a polymer called lignin which allows it to be waterproof so it can transport the water. The polymer lignin impregnates the cellulose wall and as the cells become lignified the entry of water and solutes into them is restricted.

At the same time the tonoplast breaks down and there is autolysis of the cell contents. During autolysis the cell organelles, cytoplasm and cell surface membrane are broken down by the action of enzymes and are lost, leaving an empty tube.

Water transportation in xylem vessels:

 Transpiration: water evaporated from the surface of spongy mesophyll cells and diffuses down the diffusion gradient through stomata of leaves

 Water in the spongy mesophyll leaves is replaced from the xylem, lowering hydrostatic pressure at the top of the vessel, resulting in water being drawn up from below-

transpiration stream.

 Hydrogen bonding between water molecules allows cohesion between water molecules; this keeps water as a continuous column in the xylem vessel – Cohesion-Tension Theory  Forces of adhesion occur between water molecules and the xylem cell walls.

 Root Pressure: minerals and ions moving into roots via active transport creating a concentration gradient for osmosis (water into roots)

The movement of water through xylem vessels provides a mass flow system for the transport of inorganic ions.

Nitrate ions (form of nitrogen) are needed by plants in order to make amino acids. Plants make their own amino acids from scratch using inorganic materials by a sequence of enzyme controlled reactions the nitrogen transported in the xylem is combined with organic molecules from

photosynthesis to make all 20 amino acids. Plants cannot grow without nitrate ions as they are needed in chlorophyll, nucleic acids, ATP and some growth substances.

Magnesium is needed for chlorophyll

Calcium is required for a structural role in the cell wall and permeability of the cell membrane

CORE PRACTICAL: Investigating Plant Mineral Deficiencies

1. Mexican hat plantlets into 5 solutions ( All nutrients, lacking magnesium, lacking calcium, lacking nitrogen and lacking all nutrients)

2. Cover with cling film

3. Cover test tube with black paper (stop light) 4. Place on sunny windowsill

5. After a week compare height and colour of leaves

6. Control: species of plant, volume of each solution, size of container, amount of light received

Chemical defences of plants:

Many plants have adaptations that provide chemical defences to repel and even kill animals that feed on them.Plants sometimes store toxic compounds in hairs on the surface of their leaves, such as the stinging nettle.

Many plants can be very useful as medicines. In precise doses the 'poison' that plants create can be used to deter pathogens that threaten our health.


Acrosome Reaction: 1. Sperm reaches the ovum

2. Cells surrounding the ovum release chemicals, triggering the acrosome reaction 3. Acrosome swells and fuses with the sperm cell surface membrane

4. Digestive enzymes in the acrosome are released

5. Enzymes digest through the follicle cells and zona pellucida surrounding the ovum 6. Sperm fuses with its cell surface membrane

7. Sperm nucleus enters the ovum

8. Enzymes released from the lysosomes cause the zona pellucida to thicken, preventing the entry of other sperm

9. Nuclei of the ovum and sperm fuse fertilisation Importance of fertilisation in sexual reproduction:

 restores the diploid number of chromosomes

 combines the genome from 2 cells, which is important for GENETIC VARIATION

Plant Fertilisation:  Pollen grain germinates on style

 Pollen tube grows down style towards ovary (growth controlled by tube nucleus)  Pollen grain contains 2 nuclei: tube nucleus and the generative nucleus

 On germination of pollen, generative nucleus divides by mitosis to form 2 halpoid male gamete nuclei

 2 male haploid gamete nuclei move down pollen tube

 Pollen tube grows through small pore (micropyle) into embryo sac  Both male haploid male gamete nuclei enter the embryo sac

 1 of the male gamete nuclei fuses with the egg nuclei  forms diploid zygote (divides to form the embryo)

 1 of the male gamete nuclei fuses with the 2 polar nuclei in the embryo sac,  forms triploid zygote (divides to form the seed's storage tissue  endosperm)

Stem Cells:

 undifferentiated/ unspecialised cells  which can keep dividing

 give rise to other types of cell

Types of Stem Cells:

 Totipotent: give rise to all cell types and has the potential to develop into a total individual  Pluripotent: have the potential to develop into many cell types but not all. (50 cell stage-


 Multipotent: some cells retain a certain capacity to develop into a variety of cell types

CORE PRACTICAL: Totipotency and Tissue Culture

1. Sprinkle seeds of white mustard onto damp sponge, cover with cling film and place in a warm, light place to germinate (until their seed leaves, cotyledons, start to unfold) 2. 2.5g of agar powder to 250cm³ of water. Heat and stir till dissolved

3. Pour 2cm height of molten agar into McCartney bottles. Allow to cool and solidify 4. Cut tops off just below shoot apex (growing tip) making explants

5. Push cut end of explants into agar, making sure the cotyledons don’t touch the agar 6. Cover with cling film, place in a sunny windowsill.

7. Observe over 10 days

In a plant: Most plant cells remain totipotent throughout the life of the plant.

Totipotency of plant cells allows plants to be reproduced using plant tissue culture. Small pieces of plant (explants) are sterilised and then placed on a solid agar medium with nutrients and growth


regulators. The cells then divide to form a mass of undifferentiated cells called a callus. By altering the growth regulators in the medium they can be grown into a full plant.

Uses of Stem Cells:

 To replace damaged tissues in a range of diseases. E.g. Leukaemia (cancer of the bone marrow) – kill all existing stem cells in bone marrow and replace with bone marrow transplant

 Could save/improve lives (stem cells to create organs and eyes) Sources of Stem Cells:

 Adult Stem Cells (from bone marrow) – needle – discomfort – limited range of cells

 Embryonic Stem Cells (IVF) – egg cells fertilised by sperm in a Petri dish – 4-5 days stem cells removed and embryo is destroyed (Totipotent)

Ethical Issues: Embryo’s are viable (alive) – killing a person

Regulatory Authorities: UK HFEA( Human Fertilisation and Embryology Authority)

 Proposals of research to see if they should be allowed

 Licensing and monitoring embryonic stem cell research centres- only fully trained staff are doing research

 Produce guidelines and codes of practice

 Provide information and advice to governments Uses of Mitosis:  Growth of multi-cellular organisms

 Repairing damaged tissues

 In some organisms: important for reproducing asexually producing offspring that is genetically identical to parent offspring

Stages Of Mitosis/ Cell division:

Interphase: (G1 phase/ S phase-DNA replication/ G2 phase)

So the cell has enough organelles, DNA and cytoplasm for 2 new cells


 chromosomes shorten and thicken

 centrioles move to opposite ends, forming spindle across cell between 2 poles  nuclear envelope breakdown (nucleolus disappears)


 chromosomes' centromeres attach to spindle fibres at the equator


 spindle fibres contract, pulling chromosomes apart - one chromatid of each chromosome is pulled to each pole of the spindle

 spindle breaks down


 chromosomes unravel

 nuclear envelope reforms around 2 groups of chromosomes  nucelolus reappears

CORE PRACTICAL: Observing Mitosis

1. Cut 1cm from root tip of garlic

2. Put into 2cm³ of 1M hydrochloric acid for 5 minutes 3. Put in 5cm³ water for 5 mins

4. Dry with filter paper


6. Maceration with mounted needle 7. One drop of Toluidine Blue for 2 mins 8. Cover with cover slip and blot dry 9. View under microscope

10. Calculate percentage of cells undergoing mitosis

Meiosis: (Produces gametes) 1. Each pair lines up in its homologous pairs.

2. The spindles separate the cells into 2 cells each with 1 set of chromosomes in the first stage called meiosis 1.

3. They then split up again being pulled apart again in the stage called meiosis 2 where the haploid cells are actually created

Meiosis 1: (XX) --> (X) + (X)

Meiosis 2: (X) + (X) --> (l) + (l) + (l) + (l)

Meiosis produces four daughter cells nuclei, each with half the number of chromosomes as the parent cell. The chromosome number is halved.

Two types of variation:

 Independent Assortment: 1 chromosome from each pair ends up in each daughter cell. Its random.

 Crossing Over: Homologous chromosomes pair up during the first division and all four chromatids come into contact. At these points (Chiamata/chiasma) the chromatids can break and rejoin, exchanging sections of DNA

Differential gene expression:

 Differential gene expression is caused by turning different genes on and off, by controlling transcription, which determines differentiation

 Under the right conditions, some genes are activated and some are not

 Active genes make active mRNA, which is translated into proteins within cells (by ribosome’s) controlling cell processes and determines cell structure


Development control:

The nucleus has a role in controlling the development of the individual cell and the whole multi-cellular organism's phenotype. This was first shown in classic experiments using giant algal cells. The Acetabularia mediterranea and the Acetabularia crenulata have:

 a hat  a stalk

 and a rhizoid (bottom) containing the nucleus

1. If the hats are removed and the stalks swapped, the plant develops hats with features of both species. (Intermediate hats)

2. If the intermediate hats are then removed, new ones grow that correspond to the nucleus in the rhizoid.

This shows the importance of the nucleus and chemical messengers in the development of the cell.

Dolly The Sheep: (Cloning)

1. Sheep 1: mammary cell donor sheep-mammary cells are grown in culture.

2. Sheep 2: egg cell donor sheep - the nucleus from an egg cell in the ovary is removed. 3. Cells are fused together


5. An early embryo forms

6. It’s implanted into the uterus of Sheep 3 7. Embryo develops

8. Lamb is born that is chromosomally identical to mammary cell donor Different genes are expressed:

As the embryo develops, cells differentiate: they become specialised for one function or a group of functions. Structure and function of each cell type is dependent on the proteins it synthesises. Some people demonstrated that different genes are expressed in different cells. They extracted mRNA from differentiated and undifferentiated frog cells.

 The mRNA is extracted from undifferentiated cells in early frog blastula  The mRNA in differentiated cells in later development (gastrula) is extracted  Complimentary DNA (cDNA) is made using reverse transcriptase and added  mRNA is then digested

 The cDNA and the mRNA are combined

 any mRNA that is also produced in the differentiated cells will combine with cDNA to form double strands

 free cDNA is from mRNA produced in the differentiated cells

Cells become specialised because only some genes are switched on and produce active mRNA which is translated into proteins within the cell.

Switching genes on:

In Prokaryotes:

If chemical is not present in the environment:

 The chemical repressor molecule binds to the DNA and prevents the transcription of the gene.

If chemical is present in the environment:

 The repressor molecule is prevented from binding to the DNA, and the gene is expressed. mRNA coding for the gene is transcribed and translated – producing the enzyme.

In Eukaryotes:

 Genes in uncoiled, accessible regions of the eukaryote DNA can be transcribed into mRNA.  The enzyme RNA polymerase binds to a section of the DNA adjacent to the gene to be

transcribed. This section is known as the promoter region.

 Only when the enzyme is attached to the DNA will transcription proceed.

 The gene remains switched off until the enzyme attaches to the promoter region successfully. The attachment of a regulator protein is usually also required to start transcription.

 Transcription of a gene can be prevented by protein repressor molecules attaching to the DNA of the promoter region, blocking the attachment site.

 Protein repressor molecules can attach to the regulator proteins themselves preventing them from attaching.

Gene Expression gone wrong: (FOP)

FOP (fibrodysplasia ossificans progressiva) is characterised by the growth of bones in odd places, such as within muscles and connective tissue.

FOP is an inherited condition caused by a gene mutation. In FOP one of the genes that are used to produce proteins that make bone cells is not switched off in white blood cells. So when the tissue is damaged white blood cells move to the site of damage and produce the protein that makes bone cells.

Cells organised into tissues:

Specialised cells can group themselves into a cluster working together as a tissue. Cells have specific recognition proteins, also known as adhesion molecules, on their surface membranes. Adhesion molecules help to recognise other cells like themselves and stick to them.


Cell: In multi-cellular organisms, cells are specialised for a particular function. E.g. muscle cells

and epithelial cells.

Tissue: A group of specialised cells working together to carry out 1 function. E.g. muscle cells

combining to form muscle tissue, and epithelial cells forming epithelial tissue.

Organ: A group of tissues working together to carry out 1 function. E.g. muscle, nerve and

epithelium work together in the heart.

Organ systems: A group of organs working together to carry out a particular function. E.g. the

circulatory system.

Gene expression and development:

The precise sequence of transcription and translation of genes determines the sequence of changes during development.

Master genes: control the development of each segment. They produce mRNA which is

translated into signal proteins. These proteins switch on the genes responsible for producing the proteins needed for specialisation of cells in each segment.

ABC of flowering plants: When a plant starts to flower, cells in a meristem become specialised to

form the organs that make up the flower. Most flowers contain the organs: sepals, petals, male stamens and the female carpel. These are arranged in concentric whorls.

The expression of genes in cells across the meristem determines which structures will form. When only gene A is expressed sepals form, when only gene C is expressed carpel’s form. Petals form when A and B are expressed, and stamens when B and C are expressed.

Genes and the environment: The characteristics of an organism are known as its phenotype.

Phenotype: characteristics of an organism taking into account GENOTYPE (genetic make-up)

and ENVIRONMENT (where the individual develops)

Some characteristics are controlled by the organism's genotype, with the environment having little or no effect (e.g. blood group). Discontinuous variation: When characteristics are controlled by genes at a single locus. They have phenotypes that fall into discrete groups with no overlap.

Continuous variation: Characteristics that are affected by both genotype and environment (e.g.

human height). If a graph is drawn showing the frequency distribution of the different height categories it will be bell-shaped.

Polygenic inheritance: characteristics controlled by genes at many loci

Multifactorial inheritance: characteristics controlled by several genetic factors and there is more

than one environmental factor.

Gene and Environment interactions:

There are many example of genes and environment interacting together to produce an organism's phenotype. Some examples are:

 height  hair colour  MAOA

 causes of cancer Height increase:

 Taller men have more children


 Better nutrition – increased protein  Improved health

 End of child labour  more energy for growth

 Improved heating in houses – less energy needed to heat the body- more for growth Hair Colour: (E.g. Arctic foxes)

The dark pigment in hair is called melanin which is made in melanocytes found in the skin and at the root of the hair in the follicle. These are activated by melanocyte-stimulating hormone (MSH) , which have receptors on the surface of melanocyte cells.

These melanocytes place melanin into organelles called melanosomes. The melanosomes are transferred to nearby skin and hair cells where they collect around the nucleus, protecting the DNA from harmful UV light, meaning people with darker skin have more receptors and have greater protection from UV light.

UV light increases the amount of MSH and MSH receptors making the melanocytes more active and causing the skin to darken. Hair becomes lighter due to the destruction of the melanin by UV light.

To make melanin animals use an enzyme called tyrosinase which catalyses the first step of changing the amino acid tyrosine into melanin. E.g. Himalayan rabbits have mutant alleles and tyrosinase is not made at normal body temperature, however tips of their tail, paws and ears are darker than the rest of their fur.


Monoamine oxidase A is an enzyme that catalyses the breakdown of a neurotransmitter in the brain involved in the regulation of behaviour.

It was discovered that some individuals have a rare mutation in the MAOA gene and produce no enzyme. They exhibit aggressive and sometimes violent behaviour.

This issue led to a connection between genes and violent behaviour but studies did not show a clear link.

Childhood maltreatment was associated with more antisocial behaviour as adults. Cancer:

Cancers occur when the rate of cell multiplication is faster than the rate of cell death. This causes the growth of a tumour, often in tissues with a high rate of mitosis e.g. the lung, bowel and bone marrow.Cancers are caused by damage to DNA. DNA can be easily damaged by physical factors such as UV light. It can also be damaged by chemicals, known as carcinogens, which may be in the environment or can be produced by cell metabolism. Mutations can also occur when cells divide, for example if DNA is copied incorrectly in gamete formation , an inherited form of cancer can result.

There are two types of genes that have a role in the control of the cell cycle and play a part in triggering cancer, these are:

 Oncogenes: code for the proteins that stimulate the transition from one stage of the cell cycle to the next. Mutations in these cells can lead to the cell cycle being continually active causing excessive cell division, resulting in a tumour.

 Tumour suppressor genes: produce suppressor proteins that stop the cycle, so mutations inactivating these genes mean there is no break in the cycle.

DNA damage in the embryo result in inherited cancer: — when the embryo divides by mitosis into an adult — cells giving rise to testes/ ovaries may have DNA error — therefore a gamete with faulty DNA can form

— cancer causing error could be passed on in these gametes to next generation

The environment can either cause physical or chemical damage to an individual making cancer more likely.


 Smoking severely increases the risk of a person developing lung cancer through carcinogens in tar. This tar lodges in the bronchi and causes damage to DNA in surrounding epithelial cells.

 UV light physically damages DNA cells in the skin. Moles which have been affected by UV light may grow bigger and develop into a tumour. If the tumour is not removed the cancer cells can spread to other parts of the body.

 Diet is also linked to prevention and the development of cancer. A diet rich in antioxidants which destroy radicals can help prevent cancer.

 Virus infection: a virus’ RNA may contain and oncogene. Transport of proteins in a cell:

 Nucleus: mRNA transcribe DNA

 Ribosome on rER: mRNA translated, protein made  Vesicle

 Golgi apparatus:modifies and packages proteins  Vesicle

 Cell surface membrane - out of cell by EXOCYTOSIS Sustainability

Sustainability: using resources in a way that meets the needs of the current generation without

having particularly damaging consequences on future generations.

Making products sustainable means you would need to use renewable resources (a resource that can be used indefinitely without running out) e.g. plants are renewable because harvested plants can be re-grown.

Fossil fuels are not renewable – once they’ve been used there will be no more Using plant fibres and starch:


 Ropes and fabrics can be made from plastic, which is made from oil. They can also be made from plant fibres- Bioplastics

 Making products from plant fibres is more sustainable - less fossil fuels is uses, crops can be re-grown to maintain a good supply

 Products made from plant fibres are also biodegradable – they can be broken down by microbes, plastics mainly cannot and therefore pollute the environment

 Plants are easier to grow and process (extract the fibres) than to process oil. Making them also cheaper and easier to do in developing countries


 Starch is found in all plants –crops like potatoes and corn are particularly rich of starch  Vehicle fuel is also normally made from oil, but an alternative is starch i.e. bioethanol can

be made from starch

Tensile strength: maximum load (force) it can take before it breaks.

Plant fibres are useful because they are:  long and thin

 flexible  strong 

Plant fibres can be extracted either mechanically by pulling out fibres or by digesting the surrounding tissue by retting.


CORE PRACTICAL: Working out Tensile Strength

 Attach the fibre to a clamp stand and hang a weight from the other end.  Keep adding weights, one at a time, until the fibre breaks

 Record the mass needed to break the fibre - the higher the mass, the higher the tensile strength.

 Repeat the experiment with different samples of the same fibre – increases the reliability  The fibres being tested should always be the same length

 Throughout the experiment all other variables, like temperature and humidity, must be kept constant

 Take safety measures – wear goggles to protect eyes, leave the area where weights are being attached clear so they will fall safely and don’t hurt your toes.

Historic Drug Testing---William Withering’s Digitalis soup:

 He discovered that an extract of foxgloves could be used to treat dropsy (swelling brought about by heart failure). This extract contained the drug digitalis.

 Withering made a chance observation – a patient suffering from dropsy made a good recovery after being treated with a traditional remedy containing foxgloves. Withering knew foxgloves were poisonous, so he started testing different versions of the remedy with different concentrations of digitalis – the digitalis soup

 Too much digitalis poisoned his patients, whilst too little had no effect

 It was through trial and error that he discovered the right amount to give to a patient. Modern Drug Testing:

Modern drug testing is more rigorous because the experiments are more controlled and drugs have to be tested on models before tested on live subjects to assess the potential effects. Tests are also carried out on human tissues in a lab, then tested on live animals before clinical trials are tested on humans.

Drug testing clinical trials undergoes 3 phases of testing:

 Phase one – testing a new drug on a small group of healthy individuals. It’s done to find out things like safe dosage, if there are any side effects, and how the body reacts to the drug  Phase two – the drug is now tested on a larger group of people with the disease to see how

well the drug actually works

 Phase three – the drug is now compared to existing treatments. It involves testing the drug on hundreds, even thousands of patients. Patients are randomly split into two groups (double blind trial with placebo) – one group receives the new treatment and the other group receives the existing treatment. This allows scientists to tell if the new drug is any better than existing drugs.

CORE PRACTICAL: Investigate the Antimicrobial Properties in Plants

1. Agar plates seeded with the suitable bacteria (lawn)

2. Obtain a mint leaf/garlic by crushing 3g of plant material with 10cm³ of methylated spirit 3. Shake well, and in timely intervals, for 10 minutes (30 seconds on/off vigorously

4. Pipette 0.1cm³ of the extract onto the sterile 13mm Whatman antibiotic assay paper disk– place on Petri dish

5. Allow the paper disks to dry for approximately 10 minutes on open Petri dishes

6. Make sure that temperature, amount of water, size of mint leaf, etc are kept controlled during the experiment as the conclusions drawn must be reliable.

7. Close the Petri dish and tape it.

8. Incubate the plates for 24 hours at 25ºC in an incubator

9. Observe the plates without opening them, the bacterial growth should appear cloudy, measure inhibition zone.


Conservation- Seedbanks and Zoos

Conservation: help maintain biodiversity and prevent extinction.

 The extinction of a species, or the loss of genetic diversity within a species causes a

reduction in global diversity, some species have already become extinct, like the Dodo, and there are a large number of endangered species

 Conservation involves the protection and management of those endangered species with zoos and seed banks helping to conserve genetic diversity

Seedbank – store of seeds from different species of plant. E.g. Millennium Seed Bank Project

They help conserve biodiversity by storing the seeds of endangered plants. If the plants become extinct in the wild the stored seeds can be used to grow new plants and maintain the genetic diversity with, for some species, they store a range of seeds from plants with different

characteristics (different alleles).

 Creating the cool, dry conditions needed for storage. This means seeds can be stored for a long time.

 Testing seeds for viability (the ability to grow into a plant). Seeds are planted, grown and new seeds are harvested to put back into storage.

Captive breeding – involve breeding animals in controlled environments to increase their

numbers when the animal is endangered

E.g. pandas and orang-utans are bred in captivity because their numbers are critically low in the wild

Problems with captive breeding:

 Problems breeding outside natural habitat – hard to recreate in a zoo

 Cruelty to keep the animals in captivity even if it’s done to prevent them becoming extinct

Reintroduction to the wild – the reintroduction of endangered species of animals or plants

conserve their numbers or bring them back from the brink of extinction which would also help the animals that feed on the animals or plants as part of their habitat.

The reintroduction of plants and animals also contributes to restoring habitats that have been lost, e.g. rainforests have been cut down.


 Reintroduced organisms could bring new diseases to habitats, harming other organisms living there

 Reintroduced animals may not behave as they would if they’d been raised in the wild. E.g. they may have problems finding food or communicating with wild members of their species Genetic variation is lost by

 Genetic drift: when not all the genes are passed on to the offspring by chance.

 Inbreeding depression: when two closely related individuals mate more often – causes a rise in homozygous gene types.

Advantages Disadvantages

 Cheaper to store seeds than plants  Larger numbers of seeds can be stored

because they need less space

 Less labour, to look after seeds than plants  Seeds stored anywhere, if cool and dry.  Seeds less likely to be damaged by disease,

natural disaster or vandalism than plants

 Testing the seeds for viability can be expensive and time-consuming

 Too expensive to store all types of seed and regularly test them all for viability

 Difficult to collect seeds from some plants as they may grow in remote locations


Scientific Research

Seedbanks Zoos

Research: how plants can be successfully grown from seeds, useful for reintroducing them to the wild

Research: increases knowledge about the behaviour, physiology and nutritional needs of animals. Can help conservation efforts in the wild.

Grow endangered plants for use in medical research, as new crops or materials. Don’t have to remove endangered plants from the wild.

Zoos can carry out research that is not possible for some species in the wild, e.g. nutritional or reproductive studies

Disadvantage: only studying plants from seeds in seedbank limits the data to small, interbred populations. Information gained may not be representative of wild plants

Disadvantage is that animals in captivity may act differently to those in the wild

Zoo’s help with Education – raise public awareness and interest in conserving biodiversity.

Studbooks: show the history and location of all the same species which are in captive breeding

programmes. Keep a record/database of individuals breeding history Seeds for Survival:

Plants must make sure enough of the next generation will survive. They do this by packaging a miniature plant in a protective coat with its own food supply: we call them seeds.

Inside the seed the embryo remains dormant until the conditions are suitable for restarting growth. Seeds are vital to plants, they are adapted to ensure that they:

 protect the embryo  aid dispersal

 provide nutrition for the new plant

In flowering plants the ovule is fertilised by the nucleus from a pollen grain and develops into a seed. The outer layers of the ovule are lignified creating a tough seed coat (testa) which protects the embryo within the seed. The surrounding ovary develops into a fruit which can help seed dispersal.

In some species the stored food remains outside the seed in storage tissue called endosperm. Seeds of this type are called endospermic.

Seeds come in many shapes and sizes most of which are appropriate for wide dispersal which means offspring are less likely to have to compete for nutrients with other plants.

When conditions are suitable the seed begins taking in water through a small pore in the seed coat, which triggers metabolic changes in the seed. Production of plant growth substances is switched on and these let out enzymes which mobilise stored food. Maltase and amylase break down starch into glucose which is converted to sucrose for transport to the radicle (young root) and plumule (young shoot). Proteases break down proteins in the food store to give amino acids. Lipases break down stored lipids to give glycerol and fatty acids.




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