1. A leaf in time Library activity

2. Leaves…
Leaves are the organs of photosynthesis and make all the food for a plant.
We will look at:
Outer layers (top & bottom)
Inner structure including veins (its transport system)

3. Internal structure
waxy cuticle
mesophyll
SQA-
Describe the external features and internal structure (epidermis, mesophylls, veins) of a leaf in relation to its function in gas exchange
Interpretation- a leaf has a large surface area to allow the maximum amount of light to enter the leaf.
And to expose it to as much air as possible.
A leaf is thin to allow CO2 to pass quickly to the cells which carry out photosynthesis.
And to allow O2 to leave the leaf as quickly as possible.
Thin to allow sunlight to penetrate to all cells.
Outer layer of cells on a leaf is called the epidermis.
Epidermis is transparent to allow light through.
Epidermis contains stomata which allow gases in and out.
Top layer of the cells in a leaf is called the palisade mesophyll layer
The layer of cells below the palisade layer is called the spongy mesophyll.
The spongy mesophyll cells are loosly packed with large air spaces to allow CO2 and O2
to get to and from cells quickly.
Leaf veins are made up of xylem and phloem within a short distance of every mesophyll cell to carry
food away from and water to, leaf cells.
Collect the handout ‘Leaf structure’ and add labels/notes.

4. Outer layer- upper surface
1.waxy 2.
Epidermis transparent so no chlorophyll
1. The waxy cuticle is a waterproof layer which cuts down water loss by evaporation.
2. The upper cells of the leaf make up the epidermis.
They are transparent so light passes straight through them into the next layer of cells…

5. The palisade layer contains cells with lots of chloroplasts.
mesophyll
Chloroplasts contain chlorophyll which is the chemical which absorbs the sun’s light energy.
Hence this is where most photosynthesis occurs.
The spongy layer (spongy mesophyll) contains rounded cells with many air spaces allowing CO2 to circulate and reach the palisade cells, while O2 leaves.

6. Workbook Activities Problem Solving Bioviewers Box 79
p Leaf surface and thickness
p67 Leaf layer cards- matching
Problem Solving
p78 How many stomata?
p79 Water content and dry weight.
p85 Use of cobalt choride paper
Bioviewers Box 79
The leaf of a flowering plant

7. Outer layer- bottom surface
Leaf epidermis with stomata- scanning electron microscope
SQA-
State that plants take in carbon dioxide from the air through stomata which can open and close
Interpretation- stomata are tiny pores on the surface of a leaf.
Carbon dioxide enters the leaf through stomata.
During the day stomata are open.
During the night stomata are closed.
Know that water vapour is lost through stomata
On the lower surface of the leaf there are tiny pores called stomata (singular- stoma) which open and close.
Stomata let CO2 diffuse in.
Water vapour and oxygen (O2) move out.

8. Stomata- open Workbook
Stomata have guard cells surrounding them to control their opening & closing.
When there is plenty of water (daytime) the guard cells are turgid and curved.
This opens the stomata and water can escape.
SQA- State that water vapour is lost through stomata.
Interpretation- the tiny pores (stomata) on the surface of a leaf allow water to be lost from the leaf.
Workbook
p 62 Leaf surfaces

9. Stomata- closed Workbook Activity PS
When there is little water the guard cells are flaccid and less curved.
This closes the stomata and keeps water in the leaf. This happens at night.
GUARD CELLS are only part of lower epidermis which contain chloroplasts
They control gas exchange by closing stomata in darkness, or when too much water is being lost.
Workbook Activity PS
p63 stomata behaviour p82 & 83 Leaf balance

10. General structure Flat leaf blade Thin Vast network of veins Stomata
Has large surface area
Absorbs as much sunlight & CO2 as possible
Thin
CO2, reaches inner cells easily
Vast network of veins
supplies all parts of the plant with essential substances
Structural support
Bioviewer slide set?
Prepared microscope slides?
Stomata
Most in lower surface of leaf
Gas & water exchange

11. Workbook Problem Solving
Leaf veins
Leaf veins (and roots and stems) contain the xylem and phloem tubes in vascular bundles.
They run throughout the plant, transporting various substances up and down them.
Workbook Problem Solving
p 80 Ringing a plant

12. Transport systems used for?
Plants need to allow:
Gases to get in and out of the leaves.
Water and nutrients to move into the plant from the soil.
Glucose made in photosynthesis to be carried to the rest of the plant.
SQA LO
Explain why plants need transport systems
Interpretation- water is required for photosynthesis.
Food manufacture in the leaves is needed for growth and energy by the plant.
Workbook Activity
p 61 Food transport diagram
Giant redwood trees carry water & nutrients over 100m from the soil

13. Roots
Roots have specialised cells called root hair cells, which are long and thin providing a large surface area for the uptake of water and minerals.
SQA LO

14. Into the root hair cell
Water passes from the soil into root hairs by osmosis
DEFINITION
Osmosis is the net diffusion of water across a partially permeable membrane, from a solution with a high water concentration (HWC) to one with a low water concentration (LWC).
HOW DOES IT HAPPEN?
The water in the soil has a weak solution of salts
The cell sap has a more concentrated solution
Water moves from the soil into the root hair along a water concentration gradient

15. Osmosis

16. Osmosis
When water moves into a plant cell by osmosis it increases the pressure inside the cell.
The cell walls are sufficiently strong to withstand the pressure.
It is this pressure which keeps the cells rigid (maintains their turgor) and provides support.
Transpiration is the evaporation of water from the leaves of a plant.
The transpiration stream is the movement of water up the xylem (roots-stem-leaves).
This is why plants needing water ‘droop’ and become limp- WILTED

17. Functions 1. Anchoring the plant
Why? So it is not blown / knocked over
How? The roots spread out over a large area to counterbalance the structures above the soil.
This also helps plants find water.

18. 2. Absorb essential nutrients
Why? To take up substances to survive.
How? Roots have tiny hairs on their surface which increases their surface area to maximise absorption.
Many tiny hairs branch off the main root

19. 3. Absorb water Why? Water is a raw material for photosynthesis.
A root hair shown under a microscope
Root hair cell
Root hair
Root hair cells also have thin membranes to make it easier for substances to diffuse through into the plant
Why? Water is a raw material for photosynthesis.
How? Root hairs increase surface area.

20. Transport in Flowering Plants
In flowering plants there are separate transport systems for water and nutrients.
Substances are transported in vascular bundles made up of the xylem and the phloem.
Xylem Tissue
Transports water and minerals upwards from the roots to the stem and leaves.
The Xylem is made of dead cells joined into hollow tubes. They have thick strong walls made of lignin which give the plant support.
SQA LO
Know the ways which water and food move in the xylem and phloem
Interpretation- water and minerals are carried from the roots to the leaves.
Water and minerals are carried in tubes called xylem vessels.
Food is carried from the leaves to those parts of the plant which need it for growth or energy
Or to areas where it is stored.
Food is carried in tubes called phloem.

21. Phloem tissue Phloem tissue Carries nutrients,
e.g. sugars made by photosynthesis, all round the plant.
The sugars are transported all round the plant especially to growing regions and the storage organs.
Phloem cells are alive and are made of 2 types of cells; sieve tubes and companion cells.
Sieve cell end walls have holes (pores) in them. Companion cells contain the cell nuclei.

22. Sugar cane Workbook Activity Leaf Veins are Vascular Bundles.
Vascular bundles are composed of Xylem, Phloem and Fibres which support and protect the xylem and phloem.
SQA LO
Describe the structure of phloem and xylem and identify other functions of the transport system
Interpretation- xylem and phloem are usually found close together in groups called vascular bundles.
In stem vascular bundles are round the outside.
In root the vascular bundles are in the centre.
Vascular bundles also help give the stem support.
Xylem cells are dead.
The walls of xylem have rings or spirals of a tough substance called lignin.
Phloem cells are alive.
Phloem contains two kinds of cell: sieve tubes and companion cells.
The end walls of sieve tubes have pores.
Workbook Activity
p 72 Structure of xylem and phloem.

23. Vascular bundles Workbook Activity Vascular Bundles in sugar cane.
Left: cross-section
Below: detail of one bundle
Use celery stalk.
Workbook Activity
p 73 Looking at xylem

24. Xylem & phloem in stem Bioviewers Box 78 Workbook Activity
The stem of a flowering plant
Workbook Activity
p 60 Water transport in plants

25. Position of vascular tissue in the stem
The positions are different in stems compared to roots. In a stem they are round the outside.
epidermis
xylem
phloem

26. Position of vascular tissues in the roots
epidermis
xylem
phloem
Use busy lizzie stem, prestained.
Workbook Activity
p Structure stem, root
In roots they are found in the centre.

27. What Limits photosynthesis?
Light + chlorophyll
Ingredients
Carbon dioxide + water oxygen + glucose
For photosynthesis to happen all the “ingredients” need to be present.
If there are inadequate ingredients photosynthesis will stop or slow down.
SQA LO
Explain what is meant by limiting factors and describe the main factors in the process of photosynthesis
Interpretation- a limiting factor is a factor that if in short supply can cut down or limit the rate of photosynthesis.
The main limiting factors in photosynthesis are carbon dioxide, light, temperature and water
The factor that is in shortest supply will be the one that limits the rate of photosynthesis and is called a “limiting factor”.

28. 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…

29. A Light intensity is limiting the rate of reaction A B
B CO2 is limiting the rate of reaction
C The difference between the lines is due to different temperatures.
p 74 The effect of increasing carbon dioxide
p75 The effect of increasing temperature
Workbook Activity

30. Helping plants to grow
Plants need mineral salts from the soil for healthy growth. In nature, plants die, decompose and mineral salts return to the ground. 
When crops are harvested, the plants are removed, there is no decomposition, and the quality of the soil decreases as less nutrients become available.

31. Signs of Nutrient deficiency in plants
Lack of Nitrogen causes ..
Yellowing of leaves.
leaves on lower parts of the plant may die
Weak stem meaning the plant cannot grow tall.

32. Lack of Potassium causes ….
1. Yellowing of leaves
2. Poor fruit growth.

33. Lack of Magnesium causes leaves to turn yellow from the bottom of the plant upwards
Leaf from the top of a plant
Leaf from the bottom of a plant

34. Lack of Phosphorus causes ….
1. Purpling of leaves
2. Poor root growth
3. Small plant size
Copy out the diagrams from p63 Co-ordinated Biology (second Edition) showing nutrient deficiency in plants