Photosynthesis and the carbon cycle (Study Notes)

A set of practice questions (Question and Answer format) covering key concepts from photosynthesis, plant biology, the carbon cycle, and climate change.

What are the reactants in the word equation for photosynthesis?

Water and carbon dioxide.

What are the products in the word equation for photosynthesis?

Glucose and oxygen.

What pigment captures light energy in photosynthesis?

Chlorophyll.

Where does photosynthesis mainly occur in a plant?

In the leaves, inside chloroplasts (especially in the palisade layer).

What do the prefixes in 'photo' and 'synthesis' mean?

Photo means light; synthesis means making.

What is the role of chloroplasts in photosynthesis?

They contain chlorophyll and are the site of photosynthesis.

How can you tell if a leaf has been photosynthesising by testing for starch?

Boil the leaf, decolorize with ethanol, apply iodine; blue-black indicates starch.

What are stomata and what is their function?

Tiny holes in the leaf's lower epidermis that allow gas exchange (CO2 in, O2 out).

Which mineral is needed to make chlorophyll?

Magnesium.

Which mineral provides nitrogen for proteins and chlorophyll?

Nitrate (nitrogen).

Why is photosynthesis important for life on Earth?

It provides energy by forming carbohydrates and releases oxygen; it underpins most food chains.

What is the carbon cycle?

The movement of carbon among air, living organisms, and fossil fuels through processes like photosynthesis, respiration, feeding, decomposition, and combustion.

How do fossil fuels form and why are they non-renewable?

From the remains of dead organisms subjected to heat and pressure over millions of years; they store carbon and form very slowly, making them non-renewable on human timescales.

What is combustion in the carbon cycle context?

Burning fossil fuels releasing carbon dioxide into the air.

Which processes add carbon dioxide to the atmosphere?

Respiration and combustion (and decomposition releases CO2).

Which processes remove carbon dioxide from the atmosphere?

Photosynthesis.

What are greenhouse gases and which ones are prominent?

Gases like carbon dioxide and methane that trap heat in the atmosphere; CO2 is a major greenhouse gas.

What evidence shows climate change effects on weather patterns?

More extreme weather events, changing rainfall patterns, and rising sea levels.

What asteroid event is believed to have caused mass extinctions around 65–66 million years ago?

A large asteroid impact that disrupted climate by dust blocking sunlight.

How does higher mean temperature affect sea level?

Sea level rises due to thermal expansion of water and melting ice.

What is the iodine test used for in leaves, and what would it indicate?

The iodine test detects starch; if starch is present, the leaf turns blue-black.

Which surface of a leaf often has the most stomata and why?

The lower epidermis, to reduce water loss while allowing gas exchange.

What is the function of the palisade layer in a leaf?

Contains cells that do most of the photosynthesis.

Why do plants store carbohydrates as starch?

To store energy for use later, such as at night or in low light.

What does 'yield' mean in farming?

The quantity of crop harvested.

What is the approximate percentage of oxygen in Earth’s atmosphere?

About 20%.

What is the role of magnesium and nitrate in plants?

Magnesium is needed to make chlorophyll; nitrate provides nitrogen for proteins and chlorophyll.