B2.2

Question 1

Why do multi-cellular organisms need exchange surfaces unlike uni-cellular organisms?

Answer 1

Smaller organisms have a higher SA:V ratio so nutrients can diffuse straight into them fast enough to be able to sustain life. However in multi-cellular organisms there is a lower SA:V ratio, diffusion over this distance cannot happen fast enough to meet all the cells demands so they need exchange surfaces

Question 2

What are exchange surfaces?

Answer 2

They are adapted to maximise the rate of diffusion and increase the SA:V ratio such as alveoli and villi

Question 3

How are alveoli adapted for gaseous exchange?

Answer 3

• very thin alveolus walls decrease the distance increasing the rate of diffusion - a spherical shape increases the surface area increasing the rate of diffusion - a good blood supply maintains a steep concentration gradient by removing oxygenated blood and bringing in deoxygenated blood(CO2) - ventilation (breathing in and out) also maintains a steep concentration gradient

Question 4

What is the circulatory system?

Answer 4

A transport system made up of blood vessels and the heart in which blood transports substances that are needed around the body such as glucose and oxygen for respiration and carries away waste products such as CO2

Question 5

Why is it a double circulatory system?

Answer 5

This is because blood flows through the heart twice during each circuit of the body

Question 6

How does blood flow around the body?

Answer 6

• The heart pumps oxygenated blood around the body - Oxygen and glucose diffuse into cells that need them and CO2 diffuses out of the cells into the blood - The deoxygenated blood returns to the heart and is then pumped to the lungs - In the lungs CO2 diffuses out of the blood to be removed from the body and oxygen diffuses back in - The oxygenated blood returns to the heart and the cycle repeats

Question 7

What are the 3 main types of blood vessels and how are they adapted?

Answer 7

Arteries - carry blood away from the heart under high pressure, to withstand this the artery has a thick and muscular wall which can slightly expand. It also has a small lumen. Veins - return blood to the heart (low pressure), they have valves which stops the blood going the wrong way, a large lumen and fairly thin walls Capillaries - They link arteries and veins in tissues and organs, they form a network so every cell is close to a capillary. They have semipermeable walls which are one cell thick so substances can easily move through them

Question 8

What is an advantage of having a double circulatory system?

Answer 8

As blood flows through the heart twice it is under higher pressure than a single circulatory system, this higher pressure means that materials are transported much quicker around the body which is essential for larger organisms

Question 9

What’s the heart made up of?

Answer 9

It’s made up of cardiac muscle, which doesn’t need to receive an impulse from your brain to contact. The heart contains 4 chambers separated by valves: - 2 smaller chambers at the top are atria - 2 larger chambers at the bottom are ventricles

Question 10

How does blood flow through the heart?

Answer 10

Deoxygenated blood enters the right atrium through the vena cava and is then pumped into the right ventricle. It is then pumped through the pulmonary artery to the lungs to collect oxygen. The blood then returns to the heart via the pulmonary vein into the left atrium. It’s then pumped into the left ventricle(thicker than the right as the blood needs to be pumped at a higher pressure around the body). From here or is pumped at a higher pressure around the body via the aorta

Question 11

What are 4 components that make up blood?

Answer 11

Red blood cells - biconcave cells with no nucleus that carry haemoglobin, carry oxygen and fit through the lumen of the capillary one cell at a time White blood cells - large cells that contain a nucleus, fight disease by making antibodies or by changing shape to engulf microorganisms Plasma - a straw-coloured liquid (90% water)that is used to transport many dissolved things such as waste products, hormones and glucose Platelets - tiny structures that help the blood to clot

Question 12

What are the two transport systems for a plant?

Answer 12

• Xylem transports water and mineral ions from the roots to the rest of the plant. Water diffuses into the roots via osmosis and the mineral ions are taken in using active transport. - Phloem transports sugars and dissolved food molecules from the leaves to all other areas of the plants(this is called translocation) These two tissues form a structure that is known as a vascular bundle which transports and supports a plant

Question 13

What is the structure of the xylem?

Answer 13

• made from dead xylem cells - no cell walls in between - one way flow of mineral ions and water - thick walls stuffed with lignin

Question 14

What is the structure of the phloem?

Answer 14

• made of living phloem cells - permeable sieve plates are formed at the ends - two way flow of dissolved sugars

Question 15

What is translocation?

Answer 15

When soluble sugar molecules are transported around the plant from being produced in the leaves

Question 16

How do the vascular bundles provide support to the plant?

Answer 16

• In a leaf it forms a network that supports the softer leaf tissue - In the stem they are located around the outer edge which provides it with resistance - In the roots they are found in the centre enabling the root to act as an anchor

Question 17

What is transpiration?

Answer 17

The loss of water vapour from a plants leaves

Question 18

How is water lost from a plants leaves?

Answer 18

While the stomata are open, water evaporates from cells inside the leaf into the leaf’s air spaces. This means there is a concentration gradient between the surroundings air and the air inside the leaf. Water vapour then diffuses out the leaf(high concentration) into the surrounding air(low concentration).

Question 19

What is the transpiration stream?

Answer 19

The constant flow of water from the roots, through the xylem and out of the leaves.

Question 20

How do the stomata open and close?

Answer 20

• When there is plenty of light and water the guard cells take up water by osmosis, this makes them turgid, which opens the stomata - When the conditions for photosynthesis are not good, guard cells lose water and become floppy and close, which closes the stomata

Question 21

Which factors affect the rate of transpiration?

Answer 21

You can use a potometer to measure how quickly a plant shoot takes up water - Light intensity - higher the light intensity the more stomata are open increasing the rate of transpiration until a certain point when all the stomata are open - Temperature - higher the temperature the faster water evaporates from the leaf’s cells, diffusion of water vapour becomes faster, increasing the rate of transpiration - Air movement - The faster the wind speed the faster water molecules are moved away from the leaf, increasing the concentration gradient, increasing the rate of transpiration - Humidity - The higher then humidity, the lower the concentration gradient which means the diffusion of water vapour is slower which lowers the rate of transpiration