Biology

Question 1

Explain how a leaf and its cells are adapted for photosynthesis

Answer 1

Broad and Flat - Large surface area to trap more energy

Palisade Cells - These are packed with chloroplasts to trap sunlight energy

Leaf Stomata - Microscopic pores allow for gas exchange

Guard Cells - Controls the Opening/Closing of the Stomata

Thin Cells - Reduces diffusion pathway for gas exchange

Spongy Mesophyll Tissue - Contains air spaces which increase the rate of gas exchange

Question 2

Explain the effect of removing a prey from a food web on predator populations

Answer 2

• By removing their prey, there isn’t enough food for the predators to hunt, therefore they will begin to starve and population will subsequently decrease

Question 3

Explain the effect of removing a predator from a food web on prey populations

Answer 3

• By removing predator from a population, the population of prey will therefore increase as they will be hunted less.

Question 4

Devise a method to determine the population of a named organism in a garden

Answer 4

_{^{<span><b><u>CORRECT WAY </u></b></span>(this way was in the revision guide… makes more sense in my head)}}

Take a 1m x 1m quadrat and place it in the selected region

• Count the number of (organism) in the square.
• Repeat with a different square 4 times, and average the 5 results.
• Multiply the average by (total area) to estimate the number of (organism) in the field.

Question 5

Explain how organisms in a food chain of a garden contribute to the carbon cycle

Answer 5

1. Plants respire and photsynthesise both releasing and taking in carbon
2. Animals feed off plants taking in carbon to their biomass and release it through respiration
3. When organisms die, their biomass is compressed into fossil fuels which release carbon through combustion
4. Soft tissue in the dead organism is eaten by decomposers which release carbon through respiration

Question 6

Explain how fertlisiers increase the nitrate content of the soil

Answer 6

• Fertilisers, like manure or compost, recycles the nutrients left in plant animal waste and returns them to the soil through decomposition.
• Note that proteins and urea are present in animal excretion, which can be broken down (by soil bacteria) into ammonia, then converted into useful nitrates by nitrifying bacteria.

Question 7

Explain why bacteria are important for soil fertility

Answer 7

• Bacteria is a decomposer - it releases nitrogen compounds together with carbon compounds when they decompose dead plants and animals and their wastes.
• Therefore, they release nitrogen which is required for soil fertility.

Question 8

Explain how crop rotation can increase the nitrogen content in the soil

Answer 8

• Rotating which crops are planted when in a certain area.
• This means that the root nodules of one plant rotation make the soil more fertile and useful for the next crop planted increasing the next crop’s yield
• Furthermore, the root nodules of a plant contain nitrogen-fixing bacteria, which convert nitrogen gas in the air into nitrogen compounds in the soil.

Question 9

Describe the different roles of bacteria in the nitrogen cycle

Answer 9

• Nitrogen, from the air, is taken into the plant by nitrogen-fixing bacteria
• The plant then uses this nitrogen to make proteins
• Animals eat the plant, and these proteins contribute to animal biomass, as amino acids. (note that excess amino acids = urea)
• Excretion and Death of these animals returns these animal proteins and urea to the soil, where decomposing bacteria breaks down proteins and urea and turs them into ammonia.
• Then nitrifying bacteria turns ammonia in decaying matter into nitrates.
• Sometimes, denitrifying bacteria can turn nitrates back into nitrogen gas

Question 10

Why do organisms need to respire?

Answer 10

All living things respire because they need energy for

• Moving
• Keeping Warm
• Producing and Breaking Down Substances

Question 11

Explain the importance of sweating in thermoregulation of body activities

Answer 11

• Sweating is crucial in the body’s response to hyperthermia or fever
• Sweat glands secrete a layer of sweat onto the epidermis, this layer of sweat then evaporates, transferring energy from the skin to the environment.
• Therefore, the body’s temperature cools down.

Question 12

Explain the importance of thermoregulation in homeostasis

Answer 12

Homeostasis is the maintenance of the body’s internal conditions

Thermoregulation is the control of the body’s internal temperature at 37 degrees

Therefore, thermoregulation is just one crucial aspect of homeostasis.

Maintaining a constant body temperature is important because:

• Enzymes in the body, that catalyse many reactions in the body, have an optimum temperature at which they work best
• Straying too far from this optimum temperature can cause the enzymes to denature (if temp is too high) or become inactive (if too low)

Question 13

Explain how Xylem tissue is adapted to it’s function:

(also state it’s function)

Answer 13

XYLEM:

​FUNCTION: To transport water and mineral ions

1. Thick cellulose cell walls strengthened by lignin prevents it from bursting due to the water pressure.
2. Lignin kills the xylem cells, this ensures no water is used up in cell processes.
3. End walls are also broken to create one long tube, so water flow isn’t impeded.
4. Xylem cells have no subcellular structures e.g cytoplasm, nucleus, vacuole or chloroplasts so the path of water isn’t obstructed.
5. Tiny pores allow water and mineral ions to enter and leave the xylem vessels

Question 14

Explain how phloem tissue is adapted to it’s function

(also state it’s function)

Answer 14

FUNCTION: To translocate sucrose made from the glucose and starch in photosynthesis.

ADAPTATIONS:

1. No nucleus or little cytoplasm as they aren’t needed and would be a waste of energy. They create more room for the central channel
2. Companion cells to pump have many mitochondria so they have energy to actively transport sucrose
3. Pores through whcih sucrose solution can be pumped
4. Holes in the end walls allow liquids to flow from one sieve cell to the next

Question 15

Describe how transpiration occurs

Answer 15

• Transpiration is the loss of water vapour from the leaves and stems of the plant. It is a consequence of gaseous exchange, as the stomata are open so that this can occur.

1. Water evaporates at the open stomata (pores) on the leaf surfaces
2. As water molecules are attracted to each other, when some molecules leave the plant the rest are pulled up through the xylem
3. This results in more water being taken up from the soil resulting in a continuous transpiration stream through the plant

Question 16

Explain the causes and treatment of diabetes, both:

1) Type 1
2) Type 2

Answer 16

TYPE 1 DIABETES:

CAUSES : Pancreatic cells don’t produce insulin as they have been destroyed by the body’s immune system

This means they cannot control blood glucose levels naturally

TREATMENT : A type 1 diabetic would have to inject insulin into the fat layer below the skin to reduce blood glucose levels

TYPE 2 DIABETES:

CAUSES: Insulin releasing cells don’t produce enough insulin or target organs don’t respond to insulin

TREATMENT: Lifestyle changes, such as a diet or exercise, to naturally reduce your blood glucose concentration. Some type 2 diabetics may take drugs to make organs respond to insulin

Question 17

Explain how the structure of the nephron allows filtration

Answer 17

Blood flows through a network of capillaries (glomerulus) in the bowman’s capsule

Here, the smaller molecules (water urea glucose) move into the nephron while larger particles (protein blood cells) stay

ADAPTATIONS:

• This can happen as there are microscopic pores in the glomerulus, which allow these smaller molecules to pass through whilst the larger particles stay.
• The afferent arteriole has a much larger diameter than the efferent arteriole, which causes a build up of pressure in the glomerulus.

*

Question 18

Explain how the structure of the nephron supports reabsorption of glucose

(adaptations of the nephron for selective reabsorption of glucose)

Answer 18

• Selective Reabsorption of Glucose happens at the proximal convulated tubule and the distal convulated tube.

ADAPTATIONS:

1. There is a large surface area of contact between the nephron and capillaries
2. The cell membrane of the cells lining the first convoluted tubule has tiny folds called microvilli. These increase the surface area:volume ratio of the cells.
3. Cells that have protein pumps in their cell membranes contain many mitochondria

Question 19

Explain how the structure of the nephron supports reabsorption of water

Answer 19

Water is selectively rebsorbed at the loop of Henle and the collecting duct

ADAPTATIONS:

• Collecting duct is thin and permeable to allow water to move by osmosis back into the blood

Question 20

What does urine contain and how is urea formed?

Answer 20

• Urine contains excess water, excess glucose and urea.

Urea is formed from the breaking down of amino acids in the liver.

Question 21

Explain how clomifene is used to stimulate ovulation

Answer 21

• Clomifene is a drug, containing LH and FSH
• This is used in infertility treatment, it increases the concentration of LH in the women, which promotes ovulation.

Question 22

Explain how hormones are used in IVF treatment

Answer 22

• Egg follicle maturation is stimulated by hormones, LH and FSH
• Eggs are released by many follicles and they are taken from the ovary
• Sperm cells are taken from the man
• The egg cells and sperm cells are allowed to combine in a petri dish for fertilisation
• One or two healthy embryos are re-inserted into the uterus

Question 23

Describe how changes in hormones affect:

1) The Uterus Wall
2) Ovulation
3) Menstruation

Answer 23

1. The Uterus Wall - Thickens as a result of oestrogen being produced. This thickness is maintained through the release of progesterone.
2. Ovulation - This is triggered by a spike in LH around day 14
3. Menstruation - This is triggered by the falling levels of oestrogen and progesterone, which reveal to the body that fertlisation hasn’t occured.

Question 24

Explain how oestrogen, progesterone, FSH and LH interact in the menstrual cycle

Answer 24

1. Days 1-5ish: Menstruation is when the lining of the uterus breaks down and is lost with an unfertilised egg Levels of FSH here begin to increase.
2. Days 10-12ish: The uterus lining starts to thicken again FSH increases, which stimulates the production of oestrogen from the ovaries. This is what causes the uterus lining to thicken again.
3. Days 13-15: The new egg is released from the ovary (ovulation) Oestrogen inhibits the production of FSH, but stimulates the production of LH from the pituitary gland. This spike in LH triggers ovulation around day 14.
4. Days 16-28: Uterus lining continues to thicken Following ovulation, a bundle of cells is left behind in the ovaries called the corpeus luteum. This releases progesterone, which inhibits production of both LH and FSH.
5. Day 23ish: The egg cell travels along the oviduct to the uterus
6. Falling levels of Progesterone and Oestrogen towards the end of the cycle trigger menstruation

Question 25

State the equation that relates cardiac output, stroke volume and heart rate

Answer 25

Cardiac Output = Stroke Volume x Heart Rate

Question 26

Compare the variation in stroke volumes fo an Olympic athlete and an officer worker

Answer 26

• Stroke volume is the volume of blood pushed into the aorta in each beat.
• Regular exercise increases the strength of heart muscle and ventricle size.
• Therefore, fitter people, like the Olympic athelete, will have bigger stroke volumes and their hearts can beat more slowly to achieve the same cardiac output as a less fit person.

Question 27

Describe the flow of blood through the heart

Answer 27

• Deoxygenated blood from the body enters through the vena cava
• This leaves the heart through the pulmonary artery, to the lungs where it will become oxygenated
• Then, it reenters the heart through the pulmonary veins.
• When the top chambers (atriums) are full, the muscles around them contract to push blood into the ventricles.
• The muscles in the ventricle walls then contract, forcing blood out of the heart.

Question 28

Explain adaptations of the heart for pumping blood around the body

Answer 28

• When certain parts of the heart contract, valves close to stop blood flowing the wrong way
• The left ventricle has a thicker muscle wall, contracting more strongly from the right. This allows it to pump blood into the aorta, and therefore to the entire body. Whereas, the right ventricle doesn’t need a wall that thick as it only pumps blood to the lungs.

Question 29

Describe adaptations of the lungs for gas exchange

Answer 29

• The lungs contain millions of alveoli (air sacs) which increase the surface area and so increase the rate of gas exchange
• These alveoli have a thin cell membrane which reduces the diffusion pathway for gases
• They also have a large point of contact with blood capillaries, which also increases the area in which gases can be exchanged

Question 30

Explain the importance of surface area:volume ratios in the breathing systems

Answer 30

• A larger SA:V ratio means a substance has more surface area per unit volume
• The larger a cell’s surface area, the more of a substance can diffuse in and out of it in a certain time.

However, larger organisms tend to have smaller SA:V volume ratios, therfore a cell can’t get enough raw materials fast enough. Therefore, larger organisms have organs that move substances in and out of the body.

Furthermore, SA:V ratios are used in alveoli, they have a large SA:V volume ratio, increasing the surface area and increasing the rate of gas exchange.

Question 31

Describe the factors affecting the rate of diffusion:

Answer 31

1. Surface Area - A larger surface area means more space which particles can pass, therefore the overall rate of diffusion will increase if surface increases
2. Concentration Gradient - The bigger the difference in concentrations, the steeper the concentration gradient and the faster the rate of diffusion
3. Distance - The further the particles have to diffuse, the slower the rate of diffusion

Question 32

State Fick’s Law

Answer 32

rate of diffusion ∝ (surface area x concentration difference) / thickness of membrane