Leaves and Photosynthesis What adaptations do leaves have for photosynthesis?

The Structure and Function of a Leaf Learning Objectives: 2.13: Describe how the structure of a leaf is adapted for photosynthesis, including: A large surface area B containing chlorophyll in chloroplasts to absorb light C stomata for gas exchange (carbon dioxide, oxygen and water vapour)

The structure and function of a leaf Watch the following short video about the structure and function of a leaf. While you are watching, make a note of key words and important points. Pay particular attention to the names of the different parts of the leaf. Label your diagram with the information from the video.

Plant cell cell wall cell membrane cytoplasm nucleus vacuole chloroplast

Name the structure… Function Structure Controls what goes in and out of the cell. Contains the genetic material. Surrounds the cell and gives support. Contains chlorophyll and absorbs sunlight. Contains cell sap and gives support. Where all the chemical reactions happen. cell membrane nucleus cell wall chloroplasts vacuole cytoplasm

Chloroplasts absorb sunlight

External: How leaves are adapted for efficient photosynthesis Side vein Apex Mid-rib vein Leaf stalk (petiole) Leaf blade (lamina)

Draw this table in your books Feature of leaves How it aids photosynthesis Broad, flat leaves Stomata Veins Chloroplasts Waxy layer Thin

How leaves are suited to photosynthesis Leaves are broad and flat, giving large surface area to absorb as much light as possible.

They have ‘holes’ in the leaves to allow carbon dioxide in and oxygen out. These are STOMATA. Guard cells

There are veins in the leaves to transport water and sugar around.

Many of the cells are packed with chloroplasts which contain a light trapping pigment- chlorophyll.

There is a waxy layer on top to stop water being lost from the leaf.

Thin leaves provide a short diffusion distance for carbon dioxide to reach the palisade and mesophyll cells

HT: How structure of the leaf is adapted for efficient photosynthesis • Epidermis is transparent; • Palisade layer at the top containing most of the chloroplasts; • Air spaces in the spongy mesophyll allow diffusion between stomata and photosynthesising cells; • Internal surface area / volume ratio very large.

Leaf cross section In pairs examine a slide of

Use microscopes to observe internal structure of leaves

Your notes Collect a summary sheet of the structure of a leaf Complete this sheet and check your answers with your teacher. Once it is all correct, stick this into your exercise book. These will be your notes for today’s lesson so it is important that you get this done!

Plenary – What we have learned today Test your knowledge of the words you have learned today. Collect a matching sheet and match each structure with its function.

Investigating Stomata Give the function of stomata Describe how stomata regulate gas exchange. Explain why the extent to which stomata are open is considered a ‘balancing act’ between survival and death.

Light Carbon dioxide + Water Glucose + Oxygen

Photosynthesis and Chlorphyll Learning objectives: 2.13 Describe how the structure of the leaf is adapted for photosynthesis, including: large surface area containing chlorophyll in chloroplasts to absorb light c) stomata for gas exchange (carbon dioxide, oxygen and water vapour)

Sunlight & Starch Production Cells in green plants make their own food in a process known as………. photosynthesis

Carbohydrates Carbohydrate Carbon (C) Hydrogen (H) Oxygen (O) Plants make glucose. Some of this is used immediately as an energy source and the rest is converted to starch for storage. Starch is a large molecule so it cannot leave the plant cell. Glucose and starch are carbohydrates made up of the following elements: These are: Carbon (C) Hydrogen (H) Oxygen (O) Carbohydrate

Carbohydrates You now know that glucose is converted to starch for storage Presence of starch shows that plants have first made glucose by photosynthesis

How is starch made? Small, soluble glucose molecules Large, insoluble starch molecule

Sunlight Sunlight is extremely important as it provides the energy for plants to make their own food

Chloroplasts Light energy from the sun is “trapped” or fixed by the green pigment chlorophyll Chlorophyll is found in disc-shaped structures called chloroplasts in green leaves chloroplasts

Role of Chlorophyll What is chlorophyll? Chlorophyll is a green pigment that is found in chloroplasts It captures light energy from the sun for photosynthesis

Evidence for the importance of chlorophyll Some plants have variegated leaves which have green areas containing chlorophyll White or yellow areas do not contain any chlorophyll Variegation is the appearance of differently coloured zones in the leaves of plants

Variegated leaf White area: No chlorophyll Green area: Contains chlorophyll Variegated leaf

Practical Experiment Your teacher will now take you through a practical on how to test a variegated leaf for starch Copy and complete the table below: Area of Leaf Starch Present? White Green

chlorophyll light energy chemical energy

carbon dioxide absorbed by the air Raw Materials sunlight carbon dioxide absorbed by the air water absorbed from soil

Leaf Chromatography Ever wondered why leaves change colour in the autumn? Leaves actually have different types of chlorophyll to “catch” as many different wavelengths of light as possible. When the green chlorophyll dies in the autumn, the red and yellow pigments are exposed.

Leaf Chromatography Your task is to safely carry out an experiment to separate out the different pigments. This is known as chromatography. Your teacher will demonstrate how to do this

Lesson starter Which letter is pointing to the waxy cuticle in this cross section of a leaf?

Photosynthetic pigments Plants use more than one photosynthetic pigment to absorb light. This maximises the use of energy from the Sun. These pigments include: Chlorophyll a Chlorophyll b Xanthophyll Carotene

Photosynthetic pigments Chlorophyll a is the main pigment. It absorbs light mainly in the red and blue regions of the spectrum. Chlorophyll b, xanthophyll and carotene are 'accessory pigments'. They absorb light from other regions of the spectrum and pass the energy onto chlorophyll a.

Photosynthesis and light energy Learning objectives 2.14 Demonstrate an understanding of how photosynthesis uses light energy to produce glucose and how this process can be modelled using the word equation for photosynthesis

The importance of light energy Green plants need 4 raw materials for photosynthesis to occur: Carbon dioxide Water Chlorophyll Light energy If any of these are missing, photosynthesis will not happen. The raw material that is missing becomes a limiting factor

The importance of light energy Your teacher will give you a leaf to test for starch. Some of the leaves have been covered with paper to stop light from getting to them. These leaves should not contain any starch. Other leaves were left uncovered and should contain starch. Your task is to find out which leaf you have by testing it for the presence of starch.

Limiting factors 2.15 Demonstrate an understanding of how limiting factors affect the rate of photosynthesis, including: a) light intensity b) CO2 concentration c) temperature

Measuring rate of photosynthesis with Elodea (pondweed) Upside down test tube (to collect oxygen gas) Thermometer Solution of sodium carbonate (a source of CO2) funnel elodea lamp How could the light intensity be altered? How could the temperature be altered (and kept constant)? How could the CO2 concentration be altered? How can the rate of photosynthesis be measured?

Elodea http://www.kscience.co.uk/animations/photolab.htm

Carbon Dioxide + Water Glucose + Oxygen Limiting Factors There are three limiting factors that affect the rate of photosynthesis: Light intensity Carbon dioxide concentration Temperature (remember that photosynthesis is an enzyme-controlled reaction and enzymes can be denatured at high temperatures) Carbon Dioxide + Water Glucose + Oxygen Light energy

Limiting Factors Light Intensity At this point, something other than light intensity is the limiting factor As a general rule, whatever is on the x-axis is the limiting factor on the slope of the graph At this point, light intensity is the limiting factor Light Intensity

Limiting Factors The rate of photosynthesis can be measured in the following ways: Measuring the increase in dry mass of a plant over a period of time Measuring the volume of oxygen given off over a period of time Measuring the volume of carbon dioxide taken in over a period of time

Task Complete all textbook questions on pages 66-67 Write all answers in full sentences and copy diagrams where appropriate.