B4e

Question 1

How are leaves adapted for efficient photosynthesis?

Answer 1

• adapted for diffusion
• adapted to absorb light
• leaves have a network of vascular bundles

Question 2

How are leaves adapted for diffusion?

Answer 2

• leaves are broad, so have a large surface for gases to diffuse
• leaves are thin, so CO2 and water vapour have to diffuse over short distances to photosynthesising cells
• the bottom of a leaf has stomata, letting gases in and out
• guard cells surround the stomata to control when it opens and closes, this allows guard cells to control gas exchange the spongy mesophyll layer, allowing gases to move between the stomata and photosynthesising cells. This also means there is a large surface area for gas exchange (they have very big interna surface area to volume ratio)

Question 3

How are leaves adapted to absorb light?

Answer 3

• broad, so large surface area to absorb light
• have chloroplasts, which contain chlorophyll and other photosynthesis pigments to absorb light energy
• different pigments absorb different wavelengths of light, so plant cells can make the most of the Sun’s energy by absorbing as much of it as possible
• cells with most chloroplasts are in the palisade layer, near the top of the leaf where it can get the most light

Question 4

What is a network of vascular bundles and how does this benefit leaves?

Answer 4

• vascular bundles are the transport vessels, xylem and phloem
• deliver water and nutrients to every part of the leaf
• take away the glucose produced by photosynthesis
• help support leaf structure

Question 5

What is osmosis?

Answer 5

• a type of diffusion
• net movement of water molecules across a partially permeable membrane from a region of higher concentration to a region of lower water concentration

Question 6

How does osmosis work?

Answer 6

• water molecules pass both ways because water molecules move randomly
• more water on one side than the other causes a steady net flow of water into the region with fewer water molecules
• concentrated substances will get more dilute, as if the water is trying to balance the concentration

Question 7

What are turgid cells?

Answer 7

-cells that have become plump and swollen after being well watered and drawing in water by osmosis

Question 8

Why do animal cells have to have a constant amount of water in them?

Answer 8

-animal cells don’t have inelastic cell wall
-if cell takes in too much water it bursts (lysis)
-if it loses too much water the shrivel up (crenation)
-

Question 9

What is turgor pressure?

Answer 9

• the contents of a cell pushing against the inelastic cell wall
• helps to support plant tissue

Question 10

What does flaccid mean?

Answer 10

• no water in soil causes plants to wilt
• due to cells losing water and so losing turgor pressure
• cells are said to be flaccid

Question 11

What happens if a plant is really short of water?

Answer 11

• cytoplasm inside cells starts to shrink and the membrane pulls away from the cell wall
• cell is now said to be plasmolysed
• the plant doesn’t totally lose its shape, as the inelastic cell wall keeps things in position
• it just droops a bit

Question 12

What is nm?

Answer 12

-nanometres

Question 13

What is a partially permeable membrane?

Answer 13

-one with very small holes, allowing only tiny molecules (like water) through