LEAF STRUCTURE

Question 1

How is the upper epidermis adapted for its role?

Answer 1

The waxy cuticle prevents water loss by evaporation
It also acts as a barrier for pathogens

The upper epidermis is also mostly transparent, allowing light through to the mesophyll layer for photosynthesis, and there aren’t that many chloroplasts

Question 2

How is the palisade mesophyll adapted for its role?

Answer 2

There are many plant cells, that are thin and long with a large surface area
These cells have many chloroplasts and is close to the source of light, which all helps to absorb light for photosynthesis

Question 3

How is the spongy mesophyll adapted for its role?

Answer 3

The cells are packed loosely, and there are air spaces between the cells, with fewer chloroplasts than the palisade layer
These are the gas exchange surface of the plant, absorbing CO2 and releasing O2 which diffuse through the spaces

Question 4

How are xylem and phloem adapted for their roles?

Answer 4

These are transport systems, where substances are moved through veins in the leaves
Xylem takes in water and mineral ions absorbed by the roots, to supply the mesophyll cells
The phloem takes glucose away from the mesophyll cells supplying food for cells in the plant that can’t photosynthesize

Question 5

How is the lower epidermis adapted for its role?

Answer 5

The stomata - small pores in the leaf - allow CO2 to diffuse into the leaf, and O2/water vapour to diffuse out
The guard cells can change shape to open/close the stomata, letting in CO2 during the day and letting out O2

Question 6

What is transpiration?

Answer 6

The loss of water from a plant, by evaporation and diffusion
This creates water shortage in the leaf, and water comes through the root/xylem to compensate
This creates a transpiration stream through the plant
If water runs out though, the plant goes flaccid

Question 7

What is the transpiration stream?

Answer 7

The flow of water through the plant caused by transpiration, that:
1. supplies water for leaf cells - photosynthesis
2. carries mineral ions in the water
3. plant cells kept turgid by water
4. allows evaporation from leaf surface, keeping leaf cool

Question 8

How do conditions affect transpiration rate?

Answer 8

Temperature - higher temps increase transpiration rate as water particles have more energy to evaporate/diffuse

Light intensity - more light increase rate as stomata stay open in light allowing water to escape

Humidity - the less water around the leaf, rate increases as there is a higher concentration gradient between within and outside of the plant, so more diffusion happens

Wind speed - higher wind speeds increase rate as it increases the concentration gradient between within and out of the plant, as water vapour is blown away, so more diffusion happens

Question 9

What is the full test for starch in a leaf?

Answer 9

Boil the leaf in water - stopping any chemical reactions
Boil the leaf in ethanol - removing any chloropyll
Use a hot water bath to boil the ethanol
Soak the leaf in water
Add some brown iodine solution - iodine solution goes blue-black in the presence of starch

Question 10

What do root hair cells do to absorb water?

Answer 10

Water is lost from leaves by transpiration
This creates an osmotic gradient
Water diffuses into the root hair cell from the soil with a higher conc. gradient - osmosis
This water is used for photosynthesis, maintaining turgidity and transporting mineral ions