MakingFood

Page
6

Slide 42

Vascular bundles

Vascular Bundles in sugar cane.

Left: cross-section

Below: detail of one bundle

Slide 43

Xylem & phloem in stem

Bioviewers Box 78

The stem of a flowering plant

Slide 44

Position of vascular tissue in the stem

The positions are different in stems compared to roots. In a stem they are round the outside.

Slide 45

Position of vascular tissues in the roots

In roots they are found in the centre.

Slide 46

What Limits photosynthesis?

For photosynthesis to happen all the “ingredients” need to be present.

If there are inadequate ingredients photosynthesis will stop or slow down.

The factor that is in shortest supply will be the one that limits the rate of photosynthesis and is called a “limiting factor”.

Slide 47

Factors limiting photosynthesis

Low temperature

Shortage of CO2

Shortage of light

Lack of chlorophyll

Example:

A plant has plenty of water, carbon dioxide and chlorophyll, but it is night.

Hence, photosynthesis cannot take place due to lack of light.

Light is the limiting factor.

Often this sort of information is shown in a graph…

Slide 48

A

B

C

A Light intensity is limiting the rate of reaction

B CO2 is limiting the rate of reaction

C The difference between the lines is due to different temperatures.

Slide 49

Quick Quiz 2

2. Give 2 structural features of a leaf that make it a good design for photosynthesis.

3. Why do you think that the palisade cells are near the surface of the leaf?

4. Name the cells that surround the stomatal openings.

5. The spongy mesophyll cells are loosely arranged. Explain the significance of this.

6. Which 3 factors limit the rate of photosynthesis?

1. How is glucose carried from the leaves to every part of the plant?

Transported in phloem tubes (water in xylem)

Large surface area, thin, stomata, veins

To absorb as much sunlight as possible in chloroplasts

Guard cells

Large spaces between cells allow gases to diffuse quickly

Quantity of light, carbon dioxide, temperature

Slide 50

Helping plants to grow