A leaf in time Library activity

1. A leaf in timeLibrary 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 Collect the handout ‘Leaf structure’ and add labels/notes.

4. Outer layer- upper surface 1.waxy 2. 1. The waxycuticle 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 p 66-67 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 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 p 62 Leaf surfaces 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.

9. Stomata- closed Workbook Activity PS p63 stomata behaviour p82 & 83 Leaf balance When there is little water the guard cells are flaccid and less curved. This closes the stomata and keeps waterin the leaf. This happens at night.

10. General structure Flat leaf blade 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 Stomata Most in lower surface of leaf Gas & water exchange

11. Leaf veins Workbook Problem Solving p 80 Ringing a plant 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.

12. Transport systems used for? Workbook Activity p 61 Food transport diagram • 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. 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.

14. Into the root hair cell Water passes from the soil into root hairs by osmosis 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 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).

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).

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

19. 3. Absorb water A root hair shown under a microscope Root hair cell Root hair 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 Transportswater and mineralsupwards 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.

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 p 72 Structure of xylem and phloem. Leaf Veins are Vascular Bundles. Vascular bundlesare composed ofXylem, PhloemandFibres which support and protect the xylem and phloem.

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

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

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

26. Position of vascular tissues in the roots epidermis Workbook Activity p 68-69 Structure stem, root xylem phloem In roots they are found in the centre.

27. What Limits photosynthesis? Light + chlorophyll Carbon dioxide + water oxygen + glucose Ingredients • 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 “limitingfactor”.

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. Rate Light intensity Workbook Activity p 74 The effect of increasing carbon dioxide p75 The effect of increasing temperature ALight intensity is limiting the rate of reaction A B C BCO2 is limiting the rate of reaction CThe difference between the lines is due to different temperatures.

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