GCSE · Biology · AQA · Spec 8461

Uses of glucose from photosynthesis

A leaf makes glucose all day long. If you think it all goes on energy, you've found one of its five destinations, and one of the others has a catch.

Where does the glucose go?

Five jobs for one sugar

A leaf has made glucose. For each situation, pick it, then choose what the plant does with its glucose.

Still to sort

Respiration (0)

Releases the energy a cell needs right now.

Where the line is: Respiration uses the glucose up to release energy. The other four turn it into something the plant keeps or builds with.

Insoluble starch (0)

A store for later.

Where the line is: Starch and fat or oil are both stores. Starch is the one kept as grains that don't dissolve.

Fat or oil (0)

Another store for later.

Cellulose (0)

Strengthens the cell wall.

Amino acids (0)

Joined together to build proteins.

Where the line is: This is the one route glucose can't finish on its own. Hold that thought: you'll find out why before the end of the lesson.

6 of 6 still to sort.

Once you've sorted them all, notice the big idea: the five uses aren't steps in a chain. They're five different destinations for the same glucose, and each cell sends it wherever the need is.

Watch out: Glucose isn't only fuel. Respiration is just one of the five things it can become.

Saving some for later

Reason it through

A leaf has made more glucose than its cells need right now. What can the plant do with the spare?

Link 1 of 4

First link · your turn

Does the plant have to use all that glucose up in respiration straight away?

Locked — reveal the link above first

Starch or cellulose?

Same starting point, different jobs

Starch and cellulose are both made by the plant from glucose.

Which of these is closest to what you think right now?

They're both stores. Cellulose is just a tougher kind of starch.Starch strengthens the cell wall, and cellulose is the store.They're the same substance, just found in different parts of the cell.Starch is a store for later; cellulose strengthens the cell wall.

How sure are you?

I'm sureI think soI'm guessing

They're both stores. Cellulose is just a tougher kind of starch.

This is a common misconception

You're right that both are made from glucose, but the jobs are different. Cellulose isn't kept to be used later. It's built into the cell wall and stays there to make the wall stronger. The stores are starch and fat or oil.

Starch strengthens the cell wall, and cellulose is the store.

This is a common misconception

Right two jobs, swapped round. Starch is the store: insoluble grains the plant can turn back into glucose later. Cellulose is the one that strengthens the cell wall. A handy check: the 'cell' in cellulose goes with the cell wall.

They're the same substance, just found in different parts of the cell.

This is a common misconception

Same raw material, different products. Think of a pile of bricks: some get built into a wall, some get stacked in the shed for later. The bricks are the same; what they become is not. Starch and cellulose are two different substances with two different jobs.

Starch is a store for later; cellulose strengthens the cell wall.

This matches the evidence

Exactly. Same starting point, glucose, but two different destinations: one kept as a store, one built into the structure of the cell wall.

Starch is stored for later. Cellulose strengthens the cell wall. Both start as glucose.

Here's the catch

Commit to an answer before you look.

A plant has plenty of light, water and carbon dioxide, so it's making lots of glucose. But the soil it grows in contains no nitrate at all. Can it make new protein?

Put it all together

Write it, then mark it

Describe how a plant uses the glucose it makes in photosynthesis. [6 marks]

Your answer

0 words · your answer stays on this page and is not sent anywhere.

The mark scheme

Used in respiration, to release energy. (1 mark)
Converted into insoluble starch for storage. (1 mark)
Used to make fat or oil for storage. (1 mark)
Used to make cellulose, which strengthens the cell wall. (1 mark)
Used to make amino acids for protein synthesis. (1 mark)
Nitrate ions absorbed from the soil are also needed to make proteins. (1 mark)

Model answer

Some glucose is used in respiration to release energy. Some is converted into insoluble starch, which is stored. Some is used to make fat or oil, which is also stored. Glucose is used to make cellulose, which strengthens the cell wall. It is also used to make amino acids, which are used in protein synthesis; to make proteins the plant also needs nitrate ions, which it absorbs from the soil.

Five uses plus the nitrate. If you only wrote 'energy', you've got one out of six. Check for 'insoluble' in front of starch, and for nitrate next to protein.

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

One sugar, five destinations, and one of them needs a helping hand from the soil

What you need to know

The glucose a plant makes isn't only fuel: it has five different uses.
It can be used in respiration to release energy, or turned into insoluble starch or fat or oil to store.
It can be made into cellulose to strengthen cell walls, or into amino acids to build proteins.
Making proteins also needs nitrate ions, which the plant absorbs from the soil.

The big picture

The glucose a plant makes in photosynthesis is its all-purpose raw material, and it has five uses. It can be used in respiration to release energy. It can be converted into insoluble starch for storage. It can be used to make fat or oil for storage. It can be used to make cellulose, which strengthens the cell wall. And it can be used to make amino acids for protein synthesis. Glucose contains no nitrogen, so to make proteins the plant also uses nitrate ions absorbed from the soil.

Key points

1The glucose produced in photosynthesis may be used for respiration, which releases energy for the plant's cells.

2Glucose may be converted into insoluble starch for storage. Insoluble means it doesn't dissolve in water.

3Glucose may be used to produce fat or oil for storage.

4Glucose may be used to produce cellulose, which strengthens the cell wall.

5Glucose may be used to produce amino acids for protein synthesis.

6To produce proteins, plants also use nitrate ions absorbed from the soil, because amino acids contain nitrogen and glucose does not.

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Worked example

Problem

In spring, a tree grows a burst of new leaves using starch it stored the year before. Which uses of glucose does the tree need to build those new leaves, and what else must it take in?

⚠ Watch out

Writing that the plant 'stores glucose', or leaving 'insoluble' out. The plant stores it by converting it into insoluble starch (or into fat or oil).

🧠

Memory hook

Really Sweet Food Can Achieve almost anything: Respiration, Starch, Fat or oil, Cellulose, Amino acids. The 'almost' is the A. Amino acids Also need nitrate.

✓

Check yourself

A friend says: 'Starch, fat, cellulose and protein: a plant can make every one of them from glucose alone.' Which part of that is wrong, and what would you add to fix it?

Flashcards

(9)

What does a plant get from using glucose in respiration?

Energy. Respiration releases energy from glucose, and every living cell needs it, day and night.

Which two uses of glucose give the plant a store for later?

Insoluble starch, and fat or oil.

What does 'insoluble' tell you about the starch a plant stores?

That it doesn't dissolve in water. The plant converts spare glucose into insoluble starch and keeps it as a store.

Can a plant use its starch store again later?

Yes. It can turn the starch back into glucose when it needs it.

What does cellulose do in a plant?

It strengthens the cell wall. It's part of the wall's structure, not a store.

What are amino acids used for in a plant?

Protein synthesis: amino acids are joined together to build proteins, such as enzymes.

Besides glucose, what does a plant need to make amino acids, and where does it come from?

Nitrate ions, absorbed from the soil.

Why can't glucose alone be turned into amino acids?

Glucose contains only carbon, hydrogen and oxygen. Amino acids also contain nitrogen, which comes from nitrate.

Are the five uses of glucose steps that happen one after another?

No. They're alternatives: each cell uses its glucose for whatever it needs at the time.

Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.

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Five jobs for one sugar

Same starting point, different jobs

Write it, then mark it

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