B2.2

Question 1

What is a surface area to volume ratio?

Answer 1

Smaller organisms have a high SA : volume so can rely on diffusion to exchange. Diffusion is must faster as the distance is much smaller
Larger multicellular organisms have a low SA : volume and rely on large exchange systems. Transport systems are needed as the distance is too large

Question 2

How do lungs maximise rate of diffusion of oxygen into the bloodstream?

Answer 2

Contain many alveoli which increase the SA

Question 3

How does the small intestine maximise rate of diffusion?

Answer 3

Contain villi which increase the SA

Question 4

Why do we need transport systems?

Answer 4

Once a required substance has diffused into the body it must be transported to where it is needed
Main one in animals is the circulatory system
Plants have xylem and phloem tubes

Question 5

What is a circulatory system?

Answer 5

Humans have one made up the heart and blood vessels
As blood remains within the structures it is known as a closed system

Question 6

What is a double circulatory system?

Answer 6

Blood flows through the heart twice during one circuit of the body

Question 7

How does the circulatory system work?

Answer 7

• deoxygenated blood travels to the lungs from the pulmonary artery where oxygen and glucose diffuse into the blood and it become oxygenated
• the oxygenated blood returns to the heart (via the pulmonary vein) into the left atrium
• it is pumped into the left ventricle (muscle is very thick to pump blood at high pressure to aorta) down to the head and body where the oxygen and glucose diffuses out of the blood and CO2 into the blood
• the blood is now deoxygenated
• and travels up the vena cava and into the right atrium and down to the right ventricle
  The blood is then pumped up the pulmonary artery and the cycle continues

Question 8

What are blood vessels?

Answer 8

3 main blood vessels - arteries, veins and capillaries
Tubelike structures that transport blood around the body
Contain a hollow cavity called a lumen

Question 9

What is an artery?

Answer 9

• has a thick outer wall
• thick layer of muscle and elastic fibres
• small lumen
• smooth lining
  Carry blood away from the heart under HIGH pressure

Question 10

What are veins?

Answer 10

• thin outer wall
• thin layer of muscle and elastic fibres
• large lumen
• smooth lining
  Return blood to the heart, contain valves that stop the back-flow of blood

Question 11

What are capillaries?

Answer 11

• very small lumen
• wall made of a single layer of cells
  Link arteries and veins in tissues and organs
  Form a network so every cell is close to a capillary
• semi permeable

Question 12

Why is the arterial wall thick and muscular?

Answer 12

To withstand the high pressure of blood that is pumped from the heart
Th wall expands and recoils to push the blood forward

Question 13

Why are thick walls not required for veins?

Answer 13

Blood pressure is low in the veins

Question 14

What is the heart made of?

Answer 14

Made of cardiac muscle
Contraction without receiving a nerve impulse from the brain

Question 15

What are the 4 chambers of the heart?

Answer 15

Right and left atrium
Right and left ventricle
Valves separate the chambers

Question 16

What is in blood?

Answer 16

Red blood cells - small biconcave cells that have no nucleus and contain haemoglobin to carry oxygen. Fit in the lumen of a capillary one at a time
White blood cells - make antibodies that fight off disease
Plasma - straw coloured liquid that flood cells float in. 90% water
Platelets - help blood clot

Question 17

How do plants transport materials?

Answer 17

Has two transport systems:
Xylem tissue - transports water and mineral ions from the roots to the stem, leaves and flowers. Made of dead cells, hollow lumen, and thick cell wall. No cell content so is a continuous column for water to move through
Phloem tissue - transports dissolved sugared from the leaves to all other areas of the plant. TRANSLOCATION (movement of glucose form the leaf to other parts of the plant by the phloem)
Phloem and xylem are found near each other and form a vascular bundle

Question 18

What is the structure of xylem?

Answer 18

Made of xylem cells, no cell walls
A tube which water and dissolved ions can flow through
Has thick walls stiffened with lignin
One way for molecules to travel

Question 19

What is the structure of phloem?

Answer 19

Made of living cells
Cell walls of these cells don’t fully break down but form sieve plates which allow dissolved sugars to pass through

Question 20

How do the vascular bundles provide support?

Answer 20

• in the leaf they from a network that supports the softer leaf tissue
• in the stem they are located around the outer edge to provide the stem with strength to resist breeze bending
• in the root they’re found in the centre enabling the root to act as an anchor

Question 21

What is transpiration?

Answer 21

Water moves through the xylem vessel because of transpiration
Loss of water from the plants leaves
Water lost must be replaced by the uptake through the roots

Question 22

What is the transpiration stream?

Answer 22

Constant flow of water from the roots through the xylem and out the leaves

Question 23

How does water enter the xylem?

Answer 23

Active transport of mineral ions into the root hair cells to create a lower WP so water will move in by osmosis

Question 24

How is water lost from the leaves?

Answer 24

The stomata allows CO2 to diffuse in for photosynthesis
Guard cells allow stomata to open and close
While the stomata is open water vapour can leave through the stomata by diffusion

Question 25

How does transpiration stream work?

Answer 25

Look at diagram on pg81

Question 26

Why do plants wilt?

Answer 26

If a plant loses water faster than it takes it in
Leaves collapse and droop which reduces the SA for evaporation
The stomata closes and prevents photosynthesis and loss of water
Will eventually die

Question 27

What are the factors affecting transpiration?

Answer 27

Light intensity - increases rate as more water evaporates
Temperature - water evaporates quicker, diffusion becomes more rapid
Air movement -concentration gradient increases so diffusion is faster
Humidity (quantity of water in the air) - lower humidity mean concentration gradient increases so water diffuses out quicker

Question 28

Equation for measuring rate of transpiration?

Answer 28

Rate of movement = distance/time