Plantsandphotosynthesis

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9C Plants and photosynthesis

Green and growing

Leaves and photosynthesis


Photosynthesis and the environment



Green and growing


9C Photosynthesis matters

Brian started with bare soil and a packet of seeds. Now he has tomatoes for his family all summer.

The tomatoes contain lots of chemicals that were not there at the start. Where have they come from?

What’s the role of the Sun in helping the tomatoes grow?


carbon dioxide

sunlight

oxygen

water

glucose

photosynthesis

9C The process of photosynthesis

REACTANT

REACTANTFROM AIR

FROM SOIL

USED BY PLANT

TO AIR OR USED FOR RESPIRATION

PRODUCT

PRODUCT

Where do they come from?

What are the products of the reaction?

What happens to the products?

Photosynthesis is a chemical reaction that happens in the leaf.

What are the reactants?


carbon dioxidefrom the air

waterfrom soil

photosynthesis

oxygen

glucose

out of leafthrough stomata

9C Where does the sugar go?

Plants make glucose by photosynthesis. This is how they grow.

Glucose is a sugar. But a plant is not just sugar! It makes lots of other chemicals so it can grow.

Starch is one chemical that a plant makes. A potato stores starch. How does the starch get there, when glucose is made in the leaf?

carbon dioxidefrom the air

waterfrom soil

photosynthesis

oxygen

glucose

out of leafthrough stomata some oxygen and

glucose used in respiration

cellulose for cell walls

proteins for growth and enzymes

starch for storage

fats and oils for storage


9C All mixed up

Match the reactants with their products to complete the word equations.

Respiration

carbon dioxidesugaroxygen water+ +

Photosynthesis light energy taken in

carbon dioxide water+ sugaroxygen +

carbon dioxide watersugar oxygen


9C Faster photosynthesis

How fast does a plant photosynthesise? This question is very important to farmers and growers.

We can use this apparatus to measure the rate of photosynthesis. How?

We might count the oxygen bubbles per minute, or collect the gas given off in one minute and measure its volume.

What would happen if we increased the light level?

light source

oxygen collects

test tube

water

pondweed (Elodea)

beaker

funnel


9C Faster photosynthesis

Here are some results from the pondweed experiment.

What effect does light have on the rate of photosynthesis?

What would happen if we put a layer of oil on the water?

light level bubbles of oxygen per minute

very high 24

high 22

medium 15

low 7

very low 0

This stops carbon dioxide from the air dissolving in the water.


Without light energy, the reactions of photosynthesis cannot work.

TRUE!

1. Photosynthesis only happens in the light.2. Plants make food from oxygen and sunlight.3. Photosynthesis and respiration work in opposite directions.

4. Plants look green because they contain the chemical chlorophyll.

5. Roots carry out half the photosynthesis that takesplace in a healthy oak tree.

6. Plants give out carbon dioxide when they arephotosynthesising.

True or false?

9C Photosynthesis myths?

They take in carbon dioxide. Oxygen is produced by photosynthesis.

FALSE! Photosynthesis produces glucose and oxygen, while respiration breaks them down to make carbon dioxide and water.

TRUE! Chlorophyll absorbs all the colours in light except green – we see the green light because it is reflected from the plant.

TRUE! They are vital to the plant but roots cannot carry out photosynthesis – they’re underground in the dark.

FALSE! Plants need carbon dioxide from the air and water from the soil to build sugars. Oxygen is produced in photosynthesis.

FALSE!


Leaves and photosynthesis



9C Food factories

Plants are food factories! They are adapted to carry out photosynthesis quickly. How does this help them?

Most photosynthesis happens in the leaves. Can you give three ways in which these leaves are adapted to be food factories?


9C Design a food factory

Photosynthesis needs light. You are going to design a light-catching machine.



Chloroplasts use light to make sugar.Where would you put these to make the most of the light?



Photosynthesis needs carbon dioxide. How does this gas get into the leaf?



Photosynthesis needs water. How can you get it into the leaf?


If you’re a dynamite designer, you should have a food-making factory that looks something like this:


tightly packed palisadecells full of chloroplasts

spongy mesophyll with air spaces so gases can move around

veins to bring water up from the roots, and also take sugar back down to the roots for storage

stomata to let carbon dioxide into the leaf


1. Leaves are adapted for…

a) pollination

b) photosynthesis

c) photography.

2. Stomata are...

a) holes in a leaf that can open and close to let gases in and out

b) the cells that carry out photosynthesis

c) small stones found in your stomach.

9C Quiz


3. Leaves are covered with a thin waterproof layer called the…

a) popsicle

b) cuticle

c) waxicle.

4. Leaves have a large surface area to...

a) increase the rate of reactions

b) catch the maximum amount of sunlight

c) look pretty in parks and gardens.

9C Quiz


5. Palisade mesophyll is in the upper part of the leaf because…

a) it needs to capture as much sunlight as possible

b) the lower areas were already full

c) it stops the upper surface from collapsing.

6. Spongy mesophyll has large air spaces between the cells to...

a) allow veins into the leaf

b) cut down the amount of cellulose needed to build new cell walls

c) give room for gases to move more easily.

9C Quiz


Photosynthesis and the environment



Respiration and photosynthesis are like a pair of energy twins.

9C Meet the energy twins

How do these energy twins work together to keep our atmosphere in balance?

Where would we be without sunlight and green plants?

photosynthesis respiration

oxygen +

glucose

carbon dioxide

+ water

sunlight energy

energy released


9C Food, medicines, and ...

All of our food comes originally from plants.

That’s true even if you only eat steak!

Why?

Many powerful drugs come from plants. Aspirin first came from the bark of willow trees. Powerful new anti-cancer drugs are made from yew trees.

Wood, hay and bamboo are used all over the world for building.

Linen and cotton are both fabrics made from plants.

What else can we get from plants?


The rainforest question

Rainforests are very complex ecosystems. Scientists estimate that thousands of unknown species live there.

But the people living in rainforests need to live now. They cut down the trees for building and furniture. They grow crops on the land, but this destroys the soil.

What does deforestation do to the atmosphere?

What other problems does it cause?


Rainforest answers?

What do you think?

Local people need money. They need

to harvest the forests now.

Most of the money is earned by a few rich

companies. The people who live in the forests get nothing – and they

lose their homes.

People in the rich world cut down all of their

forests centuries ago – they can’t tell people in the developing world not

to do the same!

How many future life-saving drugs have we already lost from the

rainforests? How many unknown species have

we made extinct?

Science

Plantsandphotosynthesis