Transport

Question 1

Why can unicellular organisms rely on diffusion for movement of substances in and out of the cell?

Answer 1

Unicellular organisms have a large surface area to volume ratio, therefore diffusion is fast and efficient due to the short distances required substances have to travel. Substances can diffuse directly into and out of the cell across the cell membrane, and the high speed allows the cell to stay alive.

Question 2

Why do multicellular organisms need a transport system?

Answer 2

Multicellular organisms have a small surface area to volume ratio, meaning diffusion would be slow and inefficient because of the long distances that would be required to reach every cell, therefore the organism’s cells wouldn’t get required substances (e.g. water, mineral ions and sugars) fast enough and would die.

Multicellular organisms therefore need transport systems to move substances to and from cells quickly.

Question 3

What is the structure and function of the phloem?

Answer 3

Phloem cells are alive, they join end to end, sieve plates with pores allow substances to pass through. Phloem vessels transport food materials (mainly sucrose and amino acids) made by the plant from photosynthesising leaves to non-photosynthesising regions in the roots and stem (substances can move in both directions). The movement of substances through the phloem is called translocation.

Question 4

What is the structure and function of the xylem?

Answer 4

The xylem is composed of dead cells, the ends of each cell have broken down which form long, hollow tubes. Xylem cells are strengthened by lignin and so are adapted for the transport of water in the transpiration stream. Xylem vessels transport water and minerals in ONLY one direction, from the roots to the stem and leaves (shoots). This process is called transpiration.

Question 5

What is the transpiration stream?

Answer 5

Water molecules are attracted to each other by cohesion - creating a continuous column of water up the plant. Water moves through the xylem vessels in a continuous transpiration stream from roots to leaves via the stem. Transpiration produces a tension on the water in the xylem vessels from the leaves. As water molecules are held together by cohesive forces (each individual molecule ‘pulls’ on the one below it), water is pulled up through the plant. If the rate of transpiration from the leaves increases, water molecules are pulled up the xylem vessels quicker.

Question 6

How is water absorbed by the root hair cell?

Answer 6

Root hair cells are adapted for the efficient uptake of water (by osmosis) and mineral ions (by active transport). They grow between soil particles and absorb water and minerals from the soil. Root hairs increase the surface area to volume ratio significantly. This increases the rate of the absorption of mineral ions by active transport. The high proportion of dissolved minerals and sugars in the cytoplasm (of the root hair cell) give it a low water potential, therefore water moves into the root hair cell by osmosis.

The structure of a root specifically allows it to maximise absorption of water by osmosis and mineral ions by active transport.

Question 7

Where does water evaporate from during transpiration?

Answer 7

Transpiration is defined as the loss of water vapour from the parts of the plant that are above ground (leaves, stem, flowers). Loss of water occurs through evaporation of water at the surfaces of the spongy mesophyll cells followed by diffusion of water vapour through the stomata. Evaporation happens rapidly when the stomata are open because interconnecting air spaces between the mesophyll cells and the stomata creates a large surface area.

Question 8

How is the rate of transpiration affected?

Answer 8

Transpiration is affected by air movement (wind speed), humidity, temperature and light intensity.

Question 9

How does air movement/ wind speed affect transpiration?

Answer 9

The higher the airflow/ wind speed, the greater the transpiration rate (if all other conditions are constant). The wind removes saturated water vapour from surrounding air, which creates a steep concentration gradient between the leaf and the air, creating more water loss.

Question 10

How does humidity affect transpiration?

Answer 10

An increase in humidity means decrease in transpiration. When the air is saturated with water vapour the concentration gradient is weaker, so less water is lost.

Question 11

How does light intensity affect transpiration?

Answer 11

The greater the light intensity, the greater the transpiration. Guard cells are responsive to light intensity, the stronger light intensity, the more water guard cells will absorb by osmosis. This results in them becoming turgid and allowing the stomata to open allowing for more water loss.

Question 12

How does temperature affect transpiration?

Answer 12

If temperature increases the water molecules will have more kinetic energy, causing them to move faster, which means they will evaporate more easily, so transpiration occurs at a faster rate.

Question 13

How do you use a mass potometer to measure the rate of transpiration?

Answer 13

A mass potometer measures a change in mass of a plant as a measure of the amount of water that has evaporated from the leaves and stem.

Question 14

How do you use a bubble potometer to measure the rate of transpiration?

Answer 14

A bubble potometer measures the uptake of water by a stem as a measure of the amount of water that is being lost by evaporation consequently pulling water up through the stem to replace it.

Question 15

What is the method to measure the rate of transpiration using a bubble potometer?

Answer 15

• Cut a shoot underwater
  ↳ To prevent air entering the xylem and place in tube
• Set up the apparatus as shown in the diagram and make sure it is airtight, using Vaseline to seal any gaps
• Dry the leaves of the shoot
  ↳ Wet leaves will affect the results
• Remove the capillary tube from the beaker of water to allow a single air bubble to form and place the tube back into the water
• Set up a lamp 10cm from the leaf
• Allow the plant to adapt to the new environment for 5 minutes
• Record the starting location of the air bubble
• Leave for 30 minutes
• Record the end location of the air bubble
• Change the light intensity/ humidity/etc.
• Reset the bubble by opening the tap below the reservoir
• Repeat the experiment
• Calculate the rate of transpiration by dividing the distance the bubble travelled by the time period

(The further the bubble travels in the same time period, the greater the rate of transpiration)

Question 16

What are the limitations of the potometer experiment?

Answer 16

• The potometer equipment has a leak
  ↳ Solution: Ensure that all equipment fits together rightly around the rubber bungs and assemble underwater to help produce a good seal
• The plant cutting has a blockage
  ↳ Solution: Cut the stem underwater and assemble equipment underwater to minimise opportunities for air bubbles to enter the xylem
• The potometer has shown no change during the experiment
  ↳ Solution: Use the plant cuttings as soon as they have been cut, transpiration rates may slow down when the cuttings are no longer fresh

Question 17

Blood consists of..?

Answer 17

Blood consists of red blood cells, white blood cells, platelets and plasma.

• Over half of the volume of the blood is made up of plasma (55%)
• The majority of the other half is made up of red blood cells (45%)
• The remaining fraction consists of white blood cells
  and platelets (<1%)

Question 18

What is the role of plasma?

Answer 18

Plasma is a straw coloured liquid which the other components of the blood are suspended within

Plasma is important for the transport of many substances including:
- Carbon dioxide - the waste product of respiration, dissolved in the plasma as hydrogencarbonate ions and transported from respiring cells to the lungs
- Digested food and mineral ions - dissolved particles absorbed from the small intestine and delivered to requiring cells around the body
- Urea - the waste substance produced in the breakdown of proteins by the liver. Urea is dissolved in the plasma and transported to the kidneys
- Hormones - chemical messengers released into the blood from the endocrine organs (glands) and delivered to target tissues/organs of the body
Heat energy - created in respiration (an exothermic reaction), heat energy is transferred to cooler parts of the body or to the skin where heat can be lost

Question 19

How are red blood cells adapted for the transport of oxygen?

Answer 19

Red blood cells are specialised cells which carry oxygen to respiring cells

• They are full of haemoglobin, a protein that binds to oxygen to form oxyhaemoglobin
• They have no nucleus which allows more space for haemoglobin to be packed in
• The shape of a red blood cell is described as being a ‘biconcave disc’ this shape gives them a large surface area to volume ratio to maximise diffusion of oxygen in and out

Question 20

What are the two types of white blood cells?

Answer 20

The two types of white cells are phagocytes and lymphocytes.

Question 21

What is the function and structure of phagocytes?

Answer 21

Phagocytes carry out phagocytosis by engulfing and digesting pathogens. Phagocytes have a sensitive cell surface membrane that can detect chemicals produced by pathogenic cells. Once they encounter the pathogenic cell, they will engulf it and release digestive enzymes to digest it. These are non-specific immune response.

Phagocytes can be easily recognised under the microscope by their multi-lobed nucleus and their granular cytoplasm

Question 22

What is the function and structure of lymphocytes?

Answer 22

Lymphocytes can easily be recognised under the microscope by their large round nucleus which takes up nearly the whole cell and their clear, non-granular cytoplasm.

Lymphocytes produce antibodies. Antibodies are Y-shaped proteins with a shape that is specific (complementary) to the antigens on the surface of the pathogen. This is a specific type of immune response as the antibodies produced will only fit one type of antigen on a pathogen.

Question 23

What is the function of platelets?

Answer 23

Platelets are fragments of cells that are used to clot the blood. Without platelets, there would be excessive bleeding every time you cut yourself and had a wound. By clotting, platelets reduce blood flow around the wound. It also prevents pathogens from entering your wound.

Question 24

How do vaccines work?

Answer 24

Vaccines are used to induce immunity to infectious diseases. A vaccine contains harmless versions of a pathogen

There are several different methods by which scientists ensure that vaccines contain harmless pathogens such as:
↳ Killing the pathogen
↳ Making the pathogen unable to grow or divide (attenuated vaccine)
↳ Using fragments of pathogens, rather than whole cells

Once in the bloodstream, the antigens contained within the vaccine can trigger an immune response in the following way:
Lymphocytes recognise the antigens in the bloodstream
The activated lymphocytes produce antibodies specific to the antigen encountered
Memory cells and antibodies subsequently remain circulating in the bloodstream

Question 25

What the process of long-term immunity by vaccination?

Answer 25

• Future infection by the same pathogen will trigger a response that is much faster and much larger compared to the initial response
• Due to the rapid nature of the response, the pathogen is unable to cause disease and the individual is said to be immune

Question 26

What are the four chambers of the heart?

Answer 26

There are four chambers: the left atrium and right atrium (upper chambers), and the left ventricle and right ventricle (lower chambers).

Question 27

What is the structure and function of the heart?

Answer 27

Oxygenated blood from the lungs enters the left side of the heart and is pumped to the rest of the body (the systemic circuit).

The left ventricle has a thicker muscle wall than the right ventricle as it has to pump blood at high pressure around the entire body.

Deoxygenated blood from the body enters the right side of the heart and is pumped to the lungs (the pulmonary circuit).

The right ventricle is pumping blood at lower pressure to the lungs.

A muscle wall called the septum separates the two sides of the heart.

Blood is pumped towards the heart in veins and away from the heart in arteries.

The coronary arteries supply the cardiac muscle tissue of the heart with oxygenated blood.

As the heart is a muscle it needs a constant supply of oxygen (and glucose) for aerobic respiration to release energy to allow continued muscle contraction.

Valves are present to prevent blood flowing backwards.

Question 28

What is the pathway of blood through the heart?

Answer 28

Deoxygenated blood coming from the body flows through the vena cava and into the right atrium.

The atrium contracts and the blood is forced through the tricuspid (atrioventricular) valve into the right ventricle

The ventricle contracts and the blood is pushed through the semilunar valve into the pulmonary artery

The blood travels to the lungs and moves through the capillaries past the alveoli where gas exchange takes place.
↳ Low pressure blood flow on this side of the heart prevents damage to the capillaries in the lungs.

Oxygenated blood returns via the pulmonary vein to the left atrium.

The atrium contracts and forces the blood through the bicuspid (atrioventricular) valve into the left ventricle.

The ventricle contracts and the blood is forced through the semilunar valve and out through the aorta.

Thicker muscle walls of the left ventricle produce a high enough pressure for the blood to travel around the whole body.

Question 29

How does the heart rate changes during exercise and under the influence of adreline?

Answer 29

• The heart pumps blood around the body in order to supply oxygen and glucose to respiring cells
• The blood also removes waste products from the respiring cells

During exercise, the cells of the muscles respire more rapidly in order to provide energy for muscle contraction. Respiration may be aerobic if exercise is moderate, or anaerobic is exercise is more intense. An increase in respiration means an increase in requirement for oxygen and glucose as well as an increase in production of waste products that need to be removed. The nervous system responds to this requirement by stimulating the following changes.
The volume of blood pumped out of the heart also increases.

Production of the hormone adrenaline increases heart rate as part of a ‘fight or flight’ response.

At the end of a period of exercise, the heart rate may remain high for a period of time as oxygen is required in the muscles to break down the lactic acid from anaerobic respiration. This is how the oxygen debt is paid off. The time taken for the heart rate to return to the resting rate is called the recovery time
↳ A physically fit person will have a lower resting heart rate and a shorter recovery time compared to an unfit person

Question 30

What are the risk factors for coronary heart disease?

Answer 30

There are several risk factors which will increase the chances of coronary heart disease:

• Obesity
  ↳ Carrying extra weight puts a strain on the heart
  ↳ Increased weight can lead to Type 2 diabetes which further damages your blood vessels
• High blood pressure
  ↳ This increases the force of the blood against the artery walls and consequently leads to damage of the vessels
• High cholesterol
  ↳ Speeds up the build up of fatty plaques in the arteries leading to blockages
• Smoking
  ↳ Chemicals in smoke cause an increase in plaque build up and an increase in blood pressure
  ↳ Carbon monoxide also reduces the oxygen carrying capacity of the red blood cells

Question 31

What is the structure of arteries?

Answer 31

Key features:
x- Carry blood at high pressure away from the heart
- Carry oxygenated blood (except the pulmonary artery)
- Have thick muscular walls containing elastic fibres
- Have a narrow lumen
- Blood flows through at a fast speed

The structure of an artery is adapted to its function in the following ways:
- Thick muscular walls containing elastic fibres withstand the high pressure of blood and maintain the blood pressure as it recoils after the blood has passed through
- A narrow lumen also helps to maintain high pressure

Question 32

What is the structure of veins?

Answer 32

Key features:
- Carry blood at low pressure towards the heart
- Carry deoxygenated blood (other than the pulmonary vein)
- Have thin walls
- Have a large lumen
- Contain valves
- Blood flows through at a slow speed

The structure of a vein is adapted to its function in the following ways:
- A large lumen reduces resistance to blood flow under low pressure
- Valves prevent the backflow of blood as it is under low pressure

Question 33

What is the structure of capillaries?

Answer 33

Key features:
- Carry blood at low pressure within tissues
- Carry both oxygenated and deoxygenated blood
- Have walls that are one cell thick
- Have ‘leaky’ walls
- Speed of blood flow is slow

The structure of a capillary is adapted to its function in the following ways:
- Capillaries have walls that are one cell thick (short diffusion distance) so substances can easily diffuse in and out of them
- The ‘leaky’ walls allow blood plasma to leak out and form tissue fluid surrounding cells

Question 34

What is the circulation system?

Answer 34

The circulatory system consists of a closed network of blood vessels connected to the heart
- Oxygenated blood is carried away from the heart and towards organs in arteries
- These narrow to arterioles and then capillaries as they pass through the organ
- In the organs, respiring cells use up the oxygen from the blood
- The capillaries widen to venules and finally veins as they move away from the organs
- Veins carry deoxygenated blood back towards the heart

A different network of lymphatic vessels collect all the excess tissue fluid that leaks out of the capillaries and delivers it back to the circulatory system.