9. Photosynthesis - IGCSE Coordinated Sciences - · PPT file · Web...

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What are plants used for?

How many different uses of plants can you spot?


Using plants


All living organisms need food to grow and survive.

How do plants get the food they need?

Plants are known as producers because they provide food for many other organisms.

Unlike animals, plants cannot move very much, so how do they get the food that they need?

This is because food provides raw materials for growth and energy for chemical reactions.

Without plants, other organisms would have no raw materials for growth or energy.


This means that all other organisms rely on plants.

Later experiments showed that plants actually make their own food!

This was proved to be untrue by measuring the mass of the soil in a plant pot before and after growth. The soil did not decrease in mass, even though plant mass increased.

Do plants eat soil?

It used to be thought that plants got their food from the soil.

What is the name of the process by which plants make food?

Plants are the only living organisms that can do this.


Plants make their own food by photosynthesis.

What is photosynthesis?

light energy

The word photosynthesis comes from the Greek language:

This process is a chemical reaction that uses light energy.

‘photo’ means ‘light’ ‘synthesis’ means ‘putting together’

Photosynthesis just means ‘putting together with light’.


Photosynthesis


Photosynthesis: summary

How can the process of photosynthesis be summarized in one sentence?

What is the word equation for this chemical reaction?

Photosynthesis is a chemical reaction that takes place in the chloroplasts of green plant cells, where light energy is used to convert carbon dioxide and water into glucose and oxygen.

light energy

chlorophyll

carbon dioxide + water oxygen+glucose


Photosynthesis: word equation activity


What is the symbol equation for photosynthesis?

The reaction of photosynthesis can be represented by the following equation:

CO2 H2O C6H12O2 O2+ +

Is this a balanced symbol equation?

How would you balance the equation?

6 6 6

light energy

chlorophyll


light energy

chlorophyll

What is the symbol equation for this reaction?


Word equation to symbol equation


Photosynthesis equation quiz


Does photosynthesis change the air?

The evolution of photosynthesis, hundreds of millions of years ago, was one of the biggest changes to shape the Earth.

It lowered the levels of carbon dioxide in the atmosphere and raised the levels of oxygen, which is used by most organisms for respiration. Oxygen also lead to the formation of the ozone layer, which filters out harmful UV rays.

Photosynthesis by plants caused major alterations to the atmosphere of Earth, turning it from a hot and hostile planet into one suitable for life.


Why are plants important to climate change?

Carbon dioxide is a greenhouse gas. This means it traps heat from the Earth and stops it escaping into space, like a pane of glass in a greenhouse.

Burning fossil fuels, increased travel and deforestation have caused atmospheric carbon dioxide levels to rise dangerously high.

Photosynthesis converts carbon dioxide into storable sugars and oxygen. Planting more trees could help reduce the amount of carbon dioxide in the atmosphere.

This is causing the Earth to overheat, melting the ice caps and endangering species.


How is glucose used?


How can you test for photosynthesis?

The presence of starch in a leaf can be used to show that photosynthesis has taken place.

The starch test can be used to prove that photosynthesis needs light, carbon dioxide and chlorophyll to take place.

Iodine is used to test for starch.It reacts with starch and changes colour from brown to blue-black.

How would you set up an experiment to test the conditions needed for photosynthesis?

How would you make the experiment fair and reliable?


Testing leaves for starch


Only the green areas of the leaf react with the iodine and turn blue-black. Without chlorophyll, the pale areas have been unable to produce starch and do not turn

Is chlorophyll needed for photosynthesis?

Variegated leaves have pale parts, which do not contain chlorophyll. The green parts of the leaf contain chlorophyll and are the control.

Chlorophyll cannot be removed from a plant without killing the plant. Instead, variegated leaves can be used to show chlorophyll is essential for photosynthesis.

Which areas will react with iodine?

blue-black.


Testing leaves for starch – activity


Like many reactions, photosynthesis requires enzymes.

Photosynthesis is a chemical reaction and so has a rate.

What is the rate of photosynthesis?

light

Which factors do you think affect the rate of photosynthesis?

How do these factors affect the rate of photosynthesis?

carbon dioxide temperature

Is the rate of photosynthesis always the same?


How does light affect photosynthesis?

Light energy has to be absorbed by chlorophyll for photosynthesis to take place.

The brighter the light, the more light energy there is, so will photosynthesis be faster or slower?

light energy

chlorophyll


More light energy means that photosynthesis will be faster.

If light intensity is too high plant cells can be damaged.How is photosynthesis affected if this happens?


Investigating photosynthesis – apparatus


Investigation photosynthesis - experiment


Investigation photosynthesis – results


Carbon dioxide is one of the raw materials used by plants to make their food.

Carbon dioxide and the rate of photosynthesis

The concentration of carbon dioxide in the air is actually quite low (0.03%) .

light energy

chlorophyll


More carbon dioxide means more photosynthesis, so plants make more food and grow more quickly.

Why is the concentration of carbon dioxide in commercial greenhouses often raised to about 0.1%?


Photosynthesis is controlled by enzymes, which usually work best at warmer temperatures.

Does temperature affect photosynthesis?

Does increasing the temperature always increase the rate of photosynthesis?

If it gets too hot (above 40 °C), the enzymes needed for photosynthesis begin to break down and are destroyed or denatured. The rate of photosynthesis decreases or even stops completely.


What is the ideal combination of factors for the maximum rate of photosynthesis?

What is a limiting factor?

enough light

How does restricting one of these facts affect the rate?

If one of the factors is restricted, the rate of photosynthesis will be below the maximum possible rate.

The restricted factor controls how quickly photosynthesis occurs and so limits the rate. It is called the limiting factor.

enough carbon dioxide

ideal temperature (not too hot or cold).


Light intensity and photosynthesis


Carbon dioxide and photosynthesis


Temperature and photosynthesis


Limiting factors – activity


Limiting factors in a greenhouseLimiting factors in a greenhouse


Leaves are the most efficient solar panels on Earth!

How do leaves maximise photosynthesis?

Although leaves come in a variety of shapes and sizes, they share certain features that enable the plant to maximize photosynthesis.

What does this mean?

Like solar panels, leaves convert energy from the Sun into usable chemical energy.


wide and flat – this create a large surface area to absorb as much light as possible

thin – this allows gases to reach cells easily

stomata – these are pores on the underside of leaves through which gases move in and out.

veins – these carry water to the cells and carry glucose away and also support leaves

How are leaves adapted for photosynthesis?

To increase photosynthesis, leaves have certain key features:


Structure of a leaf activity


Take a look inside a leaf


How do gases enter and leave plants?

On the underside of leaves are small holes, or pores, called stomata. A single hole is called a stoma. Each stoma is surrounded by two guard cells.

When guard cells gain water, they curve outwards. This opens the stoma, allowing gases in and out.

Losing water causes the guard cells to come closer together, closing the stoma. This stops the movement of gases, but also prevents water loss.


Leaf adaptations


Glossary (1/2)

cellulose – An insoluble carbohydrate made from glucose. It is used to make cell walls.

chlorophyll – The green pigment inside chloroplasts that is needed for photosynthesis to take place.

chloroplast – The plant cell structure where photosynthesis occurs.

cuticle – A waxy layer on the surface of the leaf that prevents water loss.

epidermis – A protective outer layer of cells found on the top and underside of leaves. This layer is clear to allow photosynthesis.

guard cells – A pair of cells that control the opening and closing of a stoma (single hole).


Glossary (2/2)palisade – A layer of cells in the leaves, which contain

lots of chloroplasts. It is the main site of photosynthesis.photosynthesis – The process by which plants use

carbon dioxide and water to make glucose and oxygen in the presence of light and chlorophyll.

spongy layer – A layer of cells that contains large spaces between cells. This allows the diffusion of gases between the stomata and palisade layer.

stoma (singular) – A single hole on the lower surface of the leaf that allows gases in and out.

stomata (plural) – Small holes in the lower surface of leaves that allow gases in and out.

variegated – A leaf containing areas without chlorophyll.


Anagrams


Multiple choice quiz

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