Biology RevisionSame genes on for four days now

Inheritance and Variation

We resemble our parents because characteristics are inherited from them. This is the process of genetic information being passed on to offspring in the sex cells/gametes which they develop from. Genetic information is stored in thread-like structures called chromosomes, which are made up of a chemical called DNA (deoxyribose nucleic acid). DNA molecules are double helix.

Humans have 46 chromosomes, 23 from the mother and 23 from the father. Every normal body cell has these 23 pairs. Each chromosome contains thousands of genes joined together. Each gene is a small section of the long DNA molecule. Different versions of the same gene are called alleles.

Asexual Reproduction Sexual reproduction

Involves one parent Offspring identical to itself No variety = clones

Male and female sex cells join Genetic information inherited Mix of characteristics = variety

Common in the smallest animals, plants and in the human body – cells dividing to grow and replace worn-out tissue.

Biology RevisionWtf they’re the same!?

Cloning

Plants: cuttings & tissue culture

Taking cuttings from the stem/leaf. Cuttings are genetically identical to the parent plant. This is quick and cheap.

Tissue culture: using a mixture of plant hormones to make a small group of cells from the parent plant to produce a big mass of identical plant cells, which are stimulated to each form a new plant. This is more expensive, but means the plants are guaranteed to have the characteristics you want.

Animals: embryonic cloning

1) Fertility hormones given to top-quality female to make her produce a lot of eggs2) Sperm taken from top-quality male to fertilise the eggs (inside the womb or in the lab)3) Each embryo is divided into individual cells, and each grow into an identical embryo4) Embryos are transferred to host mothers who have been hormone’d up for pregnancy 5) Identical cloned offspring are born – they are not biologically related to their mothers

Animals: fusion cell cloning or adult cell cloning

The most complicated form of asexual reproduction, fusion cell cloning is complete cloning of animals without sexual reproduction involved at all.

1) Take the adult cell of the animal to clone and an egg cell from another of the same species2) Remove the nucleus from both cells3) Place the nucleus from the original adult in the empty egg and give it a mild electric shock4) The new cell has been fused together and starts the process of cell division5) An embryo develops which is genetically identical to the original adult animal

Embryonic cloning works because the cells of the embryo have not yet become specialized.

This technique could be used to clone animals which have been genetically engineered to be medically useful. Species could be saved; pets or prized animals could be cloned.

One big problem is that modern cloning reduces variety in a population, meaning they are less able to survive changes in their environment in the future. future..(because none of

Biology RevisionFresh genes

Genetic Engineering

Genetic engineering involves changing the genetic material of an organism. You cut a gene from one organism using enzymes, and then transfer it to the cell of a completely different organism.Genetic engineering produces a unique set of genes which can be swapped across species.

Gene for making insulin Restriction enzyme cuts out gene Insulin gene is inserted into (from a human cell) and plasmid of bacterial DNA the plasmid

Plasmid is put back into the bacterium Exactly the right kind of insulin which then multiples many times at a constant, harvestable supply

Advantages: Genetically engineered bacteria can make exactly the right type and amounts of

proteins to be harvested as a constant supply. Engineered food can have improved growth rates, food value, reduced fat levels and

also last longer in supermarkets. Engineered plants which make their own pesticide chemicals can be produced, as can

plants which can grow well in rough parts of the world. Animals which produce life-saving human proteins in their milk. “Correcting” genetic material in humans to treat genetic diseases.

Disadvantages: No one can be completely sure what all the long-term effects might be. GM food could have some effect on human health. Insects could become pesticide-resistant if they eat a constant diet of GM plants. Genes from GM plants/animals or bacteria/viruses might spread into the environment. Designer babies – people may want to manipulate the genes of their future children to

be good-looking, clever, sporty etc.

Biology RevisionPhotosynthesis

CARBON DIOXIDE + WATER → GLUCOSE + OXYGEN6CO2 H2O 6C6H2O6 O2

Leaf Structure

Leaf cells have many chloroplasts which contain chlorophyll. Chlorophyll absorbs light energy to convert carbon dioxide and water into a sugar called glucose.

Upper epidermis: waxy cuticle; waterproof layer stops water loss

Palisade layer: palisade cells at the top of the leaf are close to the light, tightly packed together and full of chloroplasts

Spongy layer: cell not tightly packed, so there are air spaceslarge surface area available for gas exchange

Lower epidermis: guard cells open and close the stomata to control water loss/gases coming in and out

Carbon dioxide is delivered to the chloroplasts by diffusion. Photosynthesis is slowed down by the waxy cuticle adapted to prevent water loss

How Plants Affect The Atmosphere

During the day, plants both respire and photosynthesise. This means that there is a two-way traffic of oxygen and carbon dioxide both into and out of the plant.During the night, plants do not photosynthesise, but they always respire. This means when it is dark, oxygen is being taken in but not given out. Carbon dioxide is given out but not being taken in.

Plants use more carbon dioxide in photosynthesis than they produce in respiration.

They produce more oxygen by photosynthesis than they use in respiration.

The overall result is that plants put oxygen into the atmosphere. This makes it possible for animals to breathe.

Photosynthesis Respiration

Takes CO2 from the air and puts oxygen into the air. Takes oxygen from the air and puts CO2 into the air.

Day Active Active

Night

No photosynthesis Active

Limiting Factors

Light intensity

As the light intensity increases, the rate of oxygen also increases to the point where the graph levels out and stays at the same rate of reaction. At this point, something else must be the limiting factor.

Wavelength also makes a difference – blue and red lights are the best but NEVER green.

Temperature

Photosynthesis involves enzymes which are temperature sensitive, so once the temperature gets too high, and the rate of photosynthesis falls as enzymes are denatured.

The peak of the graph is the optimum temperature.

Carbon dioxide

Carbon dioxide levels are higher at night because plants are respiring but not photosynthesising. So on a sunny day, carbon dioxide is very likely the limiting factor.

Biology RevisionGlucose

Uses of Glucose

Oxygen is taken in → glucose breaks down and provides energy for cells→ carbon dioxide and water are the waste products

Glucose can be used to:

make long chains of starch for storage make cellulose for cell walls combined with nitrates to make proteins for growth be converted into lipids (fats or oils) to store in seeds combined with nutrients from the soil to make amino acids make genetic material (DNA) to replicate dividing cells

Nitrates are used to make proteins and the lack of it leads to a small plant.Magnesium is the principle molecule in chlorophyll and the lack of it leads to yellow leaves.

Transport and Storage

Phloem transports sugars from leaves to the rest of the plant for growth and storage. The phloem is made of living tissue.

Xylem carries water and mineral ions from the soil. Xylem vessels are not living.

Glucose is stored as starch (insoluble) so the soluble glucose doesn’t have an effect on the water balance of the plant. Starch is an energy store for when light levels are low. Starch is stored in tubers/bulbs. We eat some of these – potatoes, carrots and onions.

Plants respire 24 hours a day to release energyGlucose is soluble in water, starch is

Minerals and salts are taken in through active transport

Biology RevisionCell your soul to science

Animal and Plant Cells

Nucleus: controls all activities of the cell and contains instructions for making new cells or organisms

Cytoplasm is where the chemical reactions take place – importantly, respiration

Cell membrane controls the passage of substances in and out of the cell

Mitochondria, where most of the energy is released during respiration

Ribosomes, where proteins are made

Specialized Cells

Cells

Tissues

Organs

Organ systems

Whole body

Biology RevisionIn, our, in, our, shake it all about

Diffusion Confusion

Diffusion is the passive movement of molecules from the region of high concentration to a region of lower concentration. Therefore it moves down a concentration gradient.

If there is no concentration gradient then you get even distribution and no net movement – but particles still have random movement from kinetic energy.

For most efficient diffusion, you need: Large surface area Short distance Steep concentration gradient

Diffusion is faster with: Higher temperatures Lighter molecular mass Gases → liquids → solids

Osmosis...can’t think of a rhyme

Osmosis is the passive movement of water molecules through a partially permeable membrane from a region of high water potential to a region of lower water potential.

High water potential = dilute solution Low water potential = more concentrated solution

1) Cells full of water become turgid. The vacuole swells up and everything is pushedagainst the cell wall.

2) Cells in concentrated salt solutions lose waterand become flaccid.

The vacuole shrinks and the cytoplasm pulls away from the cell wall. This is plasmolysis. The spaces between the clinging cytoplasm and the cell wall are full of the outside solution.

Not so much in plant cells

Examples of diffusion include:

Gases in leavesOxygen in the lungs

Food in the gut

Biology RevisionEnergy and Eating

Food Chains/Webs

Food chains show the feeding relationships in a habitat. Energy is lost as you move up a food chain, and this limits the length of the chain

Some energy goes into growth in biomass and the production of offspring, but most is used up in other ways:

o Sunlight is reflected off leaves instead of being used for photosynthesiso Energy is lost through respiration as heato Energy is lost because of excretion and defecationo Energy is used for movement and transport

Food chains always start with producers, which are almost always green plants

The other organisms in the food chain are consumers – they all get their energy and biomass by consuming other organisms

Efficiency of food production and organic farming

Meat-eating and energy efficiency

It is far more efficient for humans to eat cereals such as wheat and barley themselves, rather than to use the cereals to feed cattle and then to slaughter the cattle for beef.

This is because the energy in the beef has already passed through two steps by the time it gets to humans, and at each step the amount of available energy is reduced.

When we eat cereals (or vegetables or fruit) the energy has only passed through one step, and there has only been one set of energy losses instead of two.

Biology RevisionBiomass

Pyramids of Biomass

Pyramids of biomass are charts that show the mass of living material at each step in food chain Most food chains are quite short because a lot of energy is lost at each step. After about three

steps, very little energy is still available for use by living organisms. This also explains why there are few organisms at the top of food chains, compared with those lower down.

A pyramid of biomass looks like pyramid 2. Note the large biomass of the one oak tree, compared with the small biomass of lots of caterpillars, indicated by the shape of the pyramid.

The wider the bar, the more biomass there is.

Pyramids of biomass always have this shape (but pyramids of numbers can be any shape).

Biomass Fuels

Biomass fuels are wood (by burning), alcohol (by fermentation) and biogas (from decay). Biomass fuels are renewable, produce less pollution and are energy self-reliant.

Biology Revision

Intensive and Organic Farming

Organic farming

Organic farming involves producing food without the need for artificial fertilisers and pesticides - this may be better for people's general health, but it may also mean crop yields are smaller. Organic food is often more expensive compared to food produced by normal 'intensive' farming methods because:

More labour is needed

The crop yields may be smaller

Organic produce may be more difficult to transport without being spoiled

Intensive Farming

Intensive farming improves the efficiency of energy transfer in food chains.

Intensive farming uses pesticides to kill pests, and herbicides to kill weeds.

More food is produced

Causes problems such as pesticides accumulation in food chains

There are ethical issues with the treatment of intensively farmed animals

Minerals, Fertiliser and Cannabis Farms

Farmers put fertiliser on crops to replace minerals lost from the soil. This is necessary because the crops are harvested as opposed to being left to decay naturally (which would then return minerals to the soil). This may mean chemical fertilisers or organic ones like bones/food waste/manure which release minerals slowly because they have to decay.

Hydroponics is controlling the growth of plants by growing them in water and then manipulating the light, temperature, carbon dioxide and mineral levels to make plants grow as fast and as big as possible. You are also able to control diseases easier. There can be huge hydroponic farms with no limiting factors of photosynthesis.

There are also hydroponic farms set up to grow cannabis. This is not relevant but it makes a flashy title.

Biology Revision

Carbon cycle

Carbon Cycle

Most of the chemicals that make up living tissue contain carbon. When organisms die, the carbon is recycled so that it can be used by future generations. This process is called the carbon cycle.

Carbon enters the atmosphere as carbon dioxide Carbon dioxide is absorbed by producers to make from respiration and combustion. carbohydrates in photosynthesis.

Animals feed on the plant passing the carbon The dead organisms are eaten by decomposers &compounds along the food chain. Most of the the carbon in their bodies is returned to the carbon they consume is exhaled as carbon dioxide atmosphere as carbon dioxide. In some conditionsformed during respiration. The animals and plants decomposition is blocked. The plant and animaleventually die. material may then be available as fossil fuel in the

future for combustion.

Biology RevisionRevision of Cell Division

Mitosis

Mitosis is a type of cell division that is used for growth and repair in all cells, and produces diploid cells (two of each chromosome, the normal number) which are identical to each other and the parent cell. This means the human body’s 46 chromosomes are copied exactly.

1) Chromosomes in the nucleus are copied

2) Each chromosome has 2 chromatids

3) The chromosomes align themselves and move towards the poles

4) The chromatids are pulled apart

5) There are now double the number of chromosomes as there was before. These also separate

6) The cell divides

Constant cell division ensures that cells never get too large. The larger the cell becomes, the smaller its surface area to volume ratio. Objects with a small surface area to volume ratio find it difficult to maintain exchange of materials with their environment. Large cells could run out of oxygen, and accumulate too much waste, such as carbon dioxide. For this reason it's more efficient for large organisms to be multicellular, rather than single-celled

Biology RevisionRevision of Cell Division

Meiosis

In sexual reproduction, cells from each parents with half the normal number of chromosomes join together to make a new cell containing both parents’ genetic material. The human gametes (egg and sperm) have 23 chromosomes which join together during fertilisation.

Meiosis is the type of cell division used in sexual reproduction. It occurs only in the testes and ovaries and produces cells that are haploid, which means they are different to each other, and to the parent cell. The cells produced have half the normal number of chromosomes.

Meiosis therefore causes genetic variation.

Biology RevisionCrap things no one ever remembers

Variables

Categoric: best described by a label, usually a word. (e.g. colours)Discrete: described in whole numbers. (e.g. number of leaves on different plants)Ordered: able to order the data but not give it an actual number. (e.g. different heights) Continuous: measured, so its value can be any number. (e.g. temperature)

An independent variable is one that we change ourselves.A dependent variable is one that we measure. A control variable is one kept constant so it is a fair test.

A conclusion is making links between variables.

Graphs

Bar charts: → Independent variable is categoric or ordered→ Dependent variable is continuous

Line graphs: → Independent variable is continuous→ Dependent variable is continuous

Scatter graphs: → like line graph, but for when you are not expecting a clear line of best fit

Reliability, Validity, Stupidity

Reliability: When results are the same or similar every time Necessary to control as many other variables as possible Repeating, discarding anomalies and calculating an average

Precision: When REPEATED results are closely grouped together Precise results are not necessarily accurate

Accuracy: When results are very close to the TRUE VALUE Using higher quality instruments and/or being more careful Repeat results for accuracy of the mean

Validity: Must be reliable and also answer the original question