Which layer of the leaf is the main site of photosynthesis?

The palisade layer, which has the most chloroplasts.

What is the function of the spongy mesophyll?

Air spaces allow gases to diffuse through the leaf.

Pores in the leaf surface that let carbon dioxide in and oxygen and water vapour out.

What happens when guard cells are swollen with water?

They curve and the stoma opens.

What does the xylem carry?

Water and minerals from the roots to the leaf.

What does the phloem carry?

Sugars made in photosynthesis, away from the leaf.

What is a limiting factor?

The factor in shortest supply that restricts the rate of photosynthesis.

Name three limiting factors of photosynthesis.

Light intensity, carbon dioxide concentration and temperature.

What does a plateau on a rate graph show?

The factor on the x-axis is no longer limiting; another factor is in shortest supply.

How is the rate measured in the pondweed investigation?

By counting the bubbles of oxygen released per minute.

Why is sodium hydrogencarbonate added to the water?

To supply carbon dioxide so it does not limit the rate.

Leaf structure and factors affecting photosynthesisIB MYP Sciences: Flashcards

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What is the function of the waxy cuticle?

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What is the function of the waxy cuticle?: It is waterproof and reduces water loss from the leaf.
Which layer of the leaf is the main site of photosynthesis?: The palisade layer, which has the most chloroplasts.
What is the function of the spongy mesophyll?: Air spaces allow gases to diffuse through the leaf.
What are stomata?: Pores in the leaf surface that let carbon dioxide in and oxygen and water vapour out.
What do guard cells do?: They open and close the stoma.
What happens when guard cells are swollen with water?: They curve and the stoma opens.
What does the xylem carry?: Water and minerals from the roots to the leaf.
What does the phloem carry?: Sugars made in photosynthesis, away from the leaf.
What is a limiting factor?: The factor in shortest supply that restricts the rate of photosynthesis.
Name three limiting factors of photosynthesis.: Light intensity, carbon dioxide concentration and temperature.
Why does the rate of photosynthesis fall above about 40 °C?: The enzymes are denatured.
What does a plateau on a rate graph show?: The factor on the x-axis is no longer limiting; another factor is in shortest supply.
How is the rate measured in the pondweed investigation?: By counting the bubbles of oxygen released per minute.
Why is sodium hydrogencarbonate added to the water?: To supply carbon dioxide so it does not limit the rate.

Exam questions on Leaf structure and factors affecting photosynthesis

A botanist in Costa Rica examines a thin slice of a leaf under a microscope. She identifies the layers of cells, working from the upper surface of the leaf downwards, and notes the structures that allow the leaf to carry out photosynthesis.
Explain how the waxy cuticle helps the leaf.2 marks
A sunflower leaf has tiny pores on its lower surface. Each pore is surrounded by a pair of guard cells that can change shape. The leaf also contains veins, which are made of xylem and phloem tissue.
Describe the role of the phloem in the leaf.2 marks
A student investigates how light intensity affects the rate of photosynthesis in a piece of pondweed. She places the pondweed in a beaker of water containing dissolved sodium hydrogencarbonate. She places a lamp at different distances from the beaker and counts the bubbles of gas released from the cut stem in one minute. She records 52 bubbles per minute with the lamp 10 cm away, 30 at 20 cm, 18 at 30 cm, 10 at 40 cm and 8 at 50 cm.
Identify the independent variable, the dependent variable and one control variable in this investigation.3 marks

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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).