Biology Unit 2 (B2)

Front 1

Name the parts of an animal cell and explain what they do.

(There are 5 to name)

Back 1

• Cell membrane - This is a thin layer around the cell. It controls the movement of substances into and out of the cell.
• Nucleus - This is a large structure inside the cell. Is contains chromosomes, which control the activities of the cell, and how it develops.
• Cytoplasm - This is a jelly-like substance containing many chemicals. Most of the chemical reactions of the cell occur here.
• Mitochondria - These are small rod-shaped structures that release energy from sugar during aerobic respiration.
• Ribosomes - These are small ball-shaped structures in the cytoplasm, where proteins are made.

Front 2

Name the 3 extra parts that plant cells have that animals cells don't.

Back 2

The plant cell has the same parts as the animal cell, but these extra parts:

• Cell wall - This is outside the cell membrane. It is made of cellulose, which is strong and supports the cell.
• Permanent vacuole - This is fluid-filled cavity. The liquid inside is called cell sap, used for support.
• Chloroplasts - These are small discs found in the cytoplasm. They contain green pigment chlorophyll. Chlorophyll traps light energy for photosynthesis.

Front 3

What are three other types of cells?

(Hint: A, B, F)

Back 3

• Algal cells - Algae are an important group of organisms, which includes seaweeds. Their cell structure is the same as plant cells.

• Bacteria cells - In bacteria cells, many of the structures are similar to those of a plant cell. But:

> the cell wall has a similar function to a plants, but it is made of different chemicals.

> there is no distinct nucleus but the cell does have DNA, which is in the form of a loop.

• Fungal cells - the structure is similar to those of plant and animal cells. Fungi are larger than bacteria and include important examples like the single-celled yeasts used in bread and beer-making.

Front 4

What are specialised cells?

Back 4

Cells in humans or plants have the same basic structure, they often carry out different jobs or functions. Cells become specialised to carry out a particular job, by developing special structures.

Front 5

Name 3 specialised cells.

Back 5

• Red blood cells - these lack most cell structures but contain large amounts of haemoglobin, which allows them to carry oxygen.

• Muscle cells - these contain contractile proteins, which allow the cell to shorten.

• Palisade cells - these contain many chloroplasts, which allow the cell to photosynthesise.

• Root hair cells - these have a long extension, which projects into the soil and increases the surface area for absorbing water.

Front 6

What is diffusion and what does it do?

Back 6

Diffusion is the net movement of particles from an area of high concentration to an area of low concentration, until the concentration evens out.

This happens in a liquid or gas where particles can move.

Front 7

What factors affect the rate of diffusion?

Back 7

• Distance - the shorter the distance for the particles to have to move, the quicker the rate of diffusion. For example, leaves are thin so carbon dioxide can move through the leaf quickly.

• Concentration gradient - particles move down a concentration gradient from a high to low concentration. The greater the difference in concentration, the faster the rate of diffusion.

• Surface area - the greater the surface area means that there is more surface over which molecules can move, so the rate is faster. For example, the lungs have a large surface area for the movement of oxygen.

Front 8

What does multicellular mean?

Back 8

Multicellular - built of many cells. For example, animal and plant cells.

Front 9

Name three examples of tissues in animals.

Back 9

Muscle tissues - these are able to contract to bring about movement.

Glandular tissues - these produce substances like enzymes and hormones.

Epithelial tissues - these tissues act as covering for parts of the body.

Front 10

Name the major organ system in the human body.

Back 10

Organs work together to form organ systems. An example of an organ system in the body is the digestive system. This is an exchange system that has two major functions in the body:

• Digestion - where food is broken down. Juices, containing enzymes, produced in glands are released into the gut to digest the food.
• Absorption - where useful molecules are taken form the gut into the blood.

Front 11

Name 5 organs that make up the digestive system.

Back 11

• Mouth
• Salivary glands - this produces a digestive juice, which is added at the mouth.
• Oesophagus
  • Stomach - this adds acids - where is digestion occurs.
• Liver - this produces bile, which helps digestion
• Pancreas - this produces a digestive juice, which is added into the small intestine.
• Small intestine - here digestion is completed, and absorption of soluble foods occur.
• Large intestine - water is absorbed from the undigested foods, which then produces faeces.
• Rectum
• Anus

Front 12

What are 3 plant organs and what is their function?

Back 12

• Stem - Supports the plant. Transport molecules through the plant.

• Leaf - Produces food by photosynthesis.

• Root - Anchors the plant. Takes up water and minerals from the soil.

Front 13

Name 3 plant tissues and explain where they are and what they do.

Back 13

• Epidermal tissues - these form a covering layer over the surface of the plant.

• Mesophyll tissue layer - inside the leaf, which contains cells loaded with chloroplasts. These cells carry out photosynthesis.

• Xylem tissues - these are made of hollow cells with strong cell walls. Stacked one above the other and form a long tube through the plant. They are found around the edge of the stem. These carry water form the roots to the leaves, ad help support the plant.

• Phloem tissues - these are found close to the xylem. These also form a long tube through the plant. These cells transport sugars from the leaves to other parts of the plant.

Front 14

What is photosynthesis and what does the plant need for it to happen?

Back 14

Photosynthesis is the process where plants make their food. They need two raw materials:

• carbon dioxide from the air
• water absorbed by the roots

They also need:

• light energy form the sun
• chlorophyll - a green pigment found in the chloroplasts in the cells of plants and algae, which absorbs the light.

Front 15

What is the equation for photosynthesis?

(Must know off by heart)

Back 15

light energy

carbon dioxide + water → glucose + oxygen

Chlorophyll

Front 16

What are two products of photosynthesis?

Back 16

There are two products of photosynthesis, which are:

• The main product, which is carbohydrate glucose
• Oxygen is a by-product of the process and is released.

Front 17

How is the leaf well adapted to be the main site of photosynthesis?

Back 17

The leaf is the main site of photosynthesis. It is well adapted for this function.

• The mesophyll contains the cells that carry out photosynthesis
• The epidermis forms a covering layer.
• The xylem brings water to the mesophyll cells.
• The phloem takes the glucose away.
• There are stomata on the lower surface to allow carbon dioxide in and oxygen out.

Front 18

How can biologists measure the rate of photosynthesis?

Back 18

• The amount of raw materials used up in a period of time.
• The amount of product made in a period of time.

Front 19

What are the 3 limiting factors of photosynthesis?

Back 19

There are three factors that limit the rate of photosynthesis. These are:

1. Availability of light - the less light there is, the slower the rate of photosynthesis.

2. A suitable temperature - temperature affects the enzyme reactions. As the temperature increases, so does the the rate. However, if the temperature becomes too high it will damage the enzymes and stop photosynthesis.

3. The amount of carbon dioxide - the less carbon dioxide, the slower the rate of photosynthesis.

Front 20

What makes greenhouses good for controlling the environment which plants grow in?

Back 20

• Clear glass to allow in as much light as possible
• Ventilation vents
• Removable netting or whitewash to reduce the intense sunlight in summer
• Electric lighting to increase hours of light during the autumn and winter
• Automatic watering system
• Gravel under the plants to allow drainage of water out of pots
• Paraffin heater burns fossil fuels. This not only adds heat to help plants grow, but also releases carbon dioxide into the greenhouse

Front 21

What are advantages and disadvantages of using a greenhouse to grow plants all year round?

(This is a past exam question (4 marks))

Back 21

Light is controlled -

ADV: Increasing light increases the rate of photosynthesis, increasing the yield, giving greater profits.

DIS: Cost of electric lighting. Cost of nets.

Temperature is controlled -

ADV: Warmth increases the rate of photosynthesis, especially during cold months. So plants can be grown out of season when they have greater value.

DIS: Glass is expensive. Cost of fuel.

Carbon dioxide -

ADV: Adding carbon dioxide from burning fossil fuels speeds up photosynthesis, increasing yield.

DIS: Cost of fuels.

Front 22

What is the distribution of a species?

Back 22

The distribution is detail of where species are found over the total area where they occur.

Front 23

What is the population of a species?

Back 23

The number of organisms of a species in a given area.

Front 24

What is the community of organisms?

Back 24

All the population of organisms that live together and interact in the same area.

Front 25

What is a relationship of organisms?

Back 25

Interaction between different species living together in the same area, such that one species affects another.

Front 26

How can biologists be accurate when sampling the environment?

Back 26

Use appropriate apparatus for the task as this will generate accurate results. Each recording should be a sufficiently large sample.

Front 27

How can biologists be reliable when sampling the environment?

Back 27

Take repeat readings. Repeats make results more reliable.

Front 28

How can biologists be fair when sampling the environment?

Back 28

Always use the same equipment for each test. Make sure that recordings are not biased. To do this, use regular points along a transect, or random sampling.

Front 29

What is a protein?

Back 29

Proteins are one of the major molecule groups that make up living things.

• They are built of amino acids.
• The amino acids are linked together in long chains.
• The chains are folded to give s specific shape.
• The shape is important for their function.
• The shape allows other molecules to fit into them.

Front 30

What are enzymes?

Back 30

Enzymes are biological catalysts that speed up the rate of chemical reactions in the body.

• They are made of proteins.
• Without them the reactions of the body would be too slow for us to survive.
• The molecule that enzymes works on is called substrate.
• They can:

> break down large molecules into small ones, for example, in digestion

> build large molecules form small ones, for example, in photosynthesis.

Front 31

How do enzymes work?

Back 31

The shape is vital for its function. The shape has an area into which substrate molecules can fit. This area is called active site.

The key to the function of the enzyme is that the active site shape is complementary to the substrate shape. This is not the same shape, but the two will fit together, like a key fits into a lock. No other substrate molecule will fit, which makes them specific.

Front 32

What makes enzymes work best?

Back 32

The way enzymes work is affected by temperature an pH.

Temperature -

• As the temperature increases, the rate of reaction increases. This is because the temperature causes the enzyme and substrate to move more and bump into each other more often.
• Eventually the rate reaches a peak called the optimum temperature.
• Above the optimum temperature, the enzymes start to damage the shape of the enzymes. This makes the enzymes become denatured.

Front 33

What is digestion?

Back 33

Digestion is the breakdown of large insoluble foods molecules into small soluble molecules that can be absorbed into the blood. This provides nutrients for us to survive.

Front 34

Why are enzymes important in digestion?

Back 34

Enzymes are important in digestion.

• They catalyse these breakdown reactions in the gut.
• They are produced by specialised cells in glandular tissue.
• They are released into the cavity of the gut.
• They then breakdown the food inside the gut.

Front 35

What is important about the pH in the stomach?

Back 35

The pH varies in the gut, and this affects which enzymes can work.

The wall of the stomach produces hydrochloric acid. Only the stomach protease can work in this pH. The acid also helps by killing bacteria that enter the gut.

Front 36

How is the acid in the small intestine neutralised?

Back 36

The acidic food entering the small intestine from the stomach is neutralised by bile.

Bile is made in the liver - stored in the gall bladder - released into the small intestine - neutralises the acid.

This results in slightly alkaline conditions, which are best for the enzymes in the small intestine.

Front 37

What are commercial enzymes used for?

Back 37

Enzymes speed up the rate of chemical reactions. So they can be very useful in:

• the home - washing powders
• industry - food production

We are able to obtain many of these enzymes from microorganisms grown in fermenters. The microbes make the enzymes and release them from their cells. We can then collect them for our use.

Front 38

What are the advantages of biological washing powders?

Back 38

Detergents are cleaning agents. Detergents like washing powders are able to remove stains from clothes. Biological washing powders contain enzymes which help in the removal of stains.

Biological washing powders are able to remove stains at lower temperatures. Most enzymes work best at 40'C. So these powders will remove stains at these low temperatures, without having to boil wash.

Front 39

What are advantages of using enzymes in industry?

Back 39

Industrial processes are expensive because of the conditions they require. Enzymes are useful in industry because they allow reaction to occur:

• at lower temperature
• al lower pressures

This reduces the need fro expensive, energy-demanding equipment.

Front 40

What are the disadvantages of using enzymes in industry?

Back 40

There are a few disadvantages of using enzymes in industry.

• The enzymes will be denatured at high temperatures. This means that their shape has changed and they can no longer work.
• They can be expensive to produce. This means that they need to save the industry a lot of money to be worth using at al.

Front 41

What are uses of enzymes in industry?

Back 41

Making baby food - Protease - pre-digests protein in baby food, making it easier for babies to digest and then absorb.

Making sugar syrup - Carbohydrates - digests cheap starch to produce sugar syrup, which can be used in foods.

Making sweeteners - Isomerases - Changes glucose to another sugar called fructose, which is sweeter.

Front 42

What is respiration?

Back 42

Respiration is the process where cells release energy from molecules like sugar. It occurs continuously in both plants and animals.

It is controlled by enzymes. It can occur in two ways:

• aerobic - with oxygen
• anaerobic - without oxygen

Front 43

What is aerobic respiration?

Back 43

Aerobic respiration requires oxygen to release the energy from sugars like glucose.

• It is very efficient, releasing a lot of energy.
• The reaction o aerobic respiration occur mainly in tiny structures in the cell called mitochondria.

Front 44

What is the equation for aerobic respiration?

Back 44

Glucose + oxygen → carbon dioxide + water

(+energy)

Front 45

What is anaerobic respiration?

Back 45

This type of respiration only occurs when there is not enough oxygen.

• it is less efficient at releasing energy than aerobic respiration.
• This is because is is an incomplete breakdown of glucose.
• The reactions occur in the cytoplasm of cells.
• This happens in the muscles during intense or sprinting activities.
• The waster product is lactic acid.

Glucose → lactic acid (+a little energy)

Front 46

What are chromosomes?

Back 46

Chromosomes are thread-like structures in the nucleus of eery cells. Each chromosome contains many pieces called genes. Chromosomes are made of a chemical called DNA. In body cells chromosomes are found in paris.

Front 47

What is mitosis?

Back 47

Body cells divide by mitosis. Before they can divide, each chromosome must make an exact copy of itself so that there will be one copy for each new cell. The chromosome then has an 'X' shape. This process is DNA replication.

Front 48

What is meiosis?

(Higher Students Only)

Back 48

Meiosis is important because is halves the number of chromosomes. When two gametes fertilise each other, the normal adult number of chromosomes is required.

(See diagram in Oxford AQA Biology Text Book - page 141)

Front 49

What are gametes?

Back 49

Body cells always have chromosomes in paris. During sexual reproduction gametes are made.

• Eggs are made in the ovaries of females.
• Sperm are made in the testes of males.

Gametes will only have one pair of chromosomes. To produce cells with only half the number of chromosomes, a second type of division is used, called meiosis.

Front 50

What are stem cells?

Back 50

Stem cells are undifferentiated cells. That means that they have not specialised as any one type of cell. These cells are made useful to scientists because they can make them divide and differentiate into cell types that they need.

Front 51

Where do we get stem cells from?

Back 51

Many plants cells do not differentiate as the plant grows. These cells can be used as stem cells to form new roots on plant cuttings.

In animals, finding stem cells is more difficult. Most animal cells differentiate at an early stage in development of the animal to perform a function within an organ.

Early embryo cells are the most useful stem cells as they can divide and develop into any type of cell we want. As the animal matures, cell division is mainly restricted to repair and replacement.

Front 52

What do doctors hope they can use stem cells for?

Back 52

Doctors hope to be able to treat a number of medical conditions with stem cells, such as:

• Parkinson's disease - by replacing damaged cells in the brain
• spinal injuries - replacing damaged nerves in the spine
• organ creation - for transplant
• diabetes - replacing damaged pancreas cells

Front 53

Who was Mendel, and what was his work?

Back 53

Gregor Mendel was born in 1822. He made a number of startling observations, which form the basis of our understanding of genetics. However, the importance of his work was not realised until his death.

Mendel carried out many breeding experiments on pea plants, controlling the transfer of pollen from one plant to another. He was controlling the crossing of alleles, although he did not realise it. He worked at a time when scientists had not discovered chromosomes and had not linked inheritance to them.

Front 54

What was Mendels theory?

Back 54

• He thought that inheritance of a characteristic was controlled by factors, which we now call genes.
• He worked out that the factors must be in paris in the adult cell.
• Only one of the factors would be in the gamete.
• The offspring would contain two factors, one from each parent.
• He was able to predict to outcome of crosses, just as we have shown above.
• The ratio of 3:1 in the F2 is now called a mendelian ratio.
• Finally his work was understood about 40 years later when other scientists could explain his results using genes.

Front 55

What does Homozygous mean?

(Higher Students Only)

Back 55

Here the genotype has identical alleles, for example SS - in a genetic diagram.

Front 56

What does Heterozygous mean?

(Higher Students Only)

Back 56

here the genotype has different alleles, for example, Ss - in a genetic diagram

Front 57

What is the genetic code?

Back 57

Each gene works by coding for the sequence of amino acids in a protein.

• The genetic code is contained in a sequence of bases in the DNA molecule.
• There are four different bases: A, T, C, and G.
• Each gene is made of hundreds of bases in a sequence.
• The cell reads the bases sequence, three bases at a time.
• Each set of three bases is called a triplet.
• Each triplet codes for a specific amino acid.
• Each specific amino acid is joined to the next, and gradually builds a protein.
• The order of the amino acids is determined by the sequence of bases in the DNA.

Front 58

What is DNA fingerprinting used for?

Back 58

Everyone's DNA is unique, apart from identical twins. This fact can be used to identify individuals. The technique of DNA fingerprinting was developed in the 1980s and has two major uses.

• to establish family connections like paternity.
• to identify a criminal from evidence found at a crime scene.

The DNA sample collected is cut by enzymes, and separated to produce a series of bands on a gel. Scientists just need to match the bands to make an identification.

Front 59

Name two inherited disorders.

(Hint: P, Cf)

Back 59

Polydactyly - This is a condition where additional digits develop on the hands or feet. It is caused by a dominant allele, and can then be passed on by on parent who has the disorder.

Cystic fibrosis - This is a disorder of the cell membranes. It results in mucus build up in the lungs. It can make sufferers more vulnerable to chest infections. Other organs like the pancreas can be affected, which might affect the digestive process.

Front 60

What is embryo screening and what is is used for?

Back 60

If both parents carry the cystic fibrosis allele, or any other genetic disorder, they may decide that they want children that are free of the disorders. To do this they would use in vitro fertilisation (IVF) to produce embryos. These embryos can be screened, and only those free of the disorder would be implanted.

Front 61

What are the advantages and disadvantages of embryo screening?

Back 61

Advantages:

• The children won't have cystic fibrosis.
• the cystic fibrosis allele won't be passed on to the next generation.
• Saves money in the NHS because there will be fewer sufferers to treat.

Disadvantages:

• Embryos with cystic fibrosis allele are discarded, so we are discarding life, is this ethical?
• Some people withe the genetic disorder feel it is discrimination against them.

Front 62

What is evolution?

Back 62

Evolutions is a gradual change in an organism over time.

Front 63

What are 4 types of fossils?

Back 63

• Remains of hard parts of animals like bones, which do not easily decay.
• Remains of organisms that have not decayed because a condition for decay is absent.
• Parts that are replaced by other materials, such as minerals.
• Preserved traces of organisms such as foot prints, burrows, and marks in the soil from roots.

Front 64

What are four causes of extinction?

Back 64

1. Changes to the environment over time - some organisms cannot adapt to changes. Some changes could be global temperatures.
2. New predators - A more efficient predator hunts a population to extinction.
3. New diseases - Some diseases are so virulent that they destroy a population. Such as the elm tree is almost extinct because of the Dutch elm disease.
4. New competitors - A new species may out-compete and existing one, for example, the grey squirrel, reducing the distribution of the red.
5. A single catastrophic event - Major global events such as an asteroid impacts and volcanic eruptions dramatically change the environment.
6. Speciation - As evolution naturally produces new varieties, some will be better adapted, and older versions may die out.

Front 65

What is speciation, and how does it work?

Back 65

Speciation is where one species evolves into two new species.

How new species form:

• Isolation - The population becomes divided into two groups by some kind of barrier like a new mountain range.
• Genetic variation - Variations in characteristics develop in each separated population, caused by alleles.
• Natural selection - In two populations, different characteristics will be favoured in the different conditions. The individuals with these characteristics will survive. The alleles are passed onto the next generation.
• Speciation - Over time, each group of the population becomes so different. Eventually they cannot interbreed, and so have formed a new species.