Photosynthesis

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Lesson notes

What is Photosynthesis?

Photosynthesis is a **chemical reaction** that produces **glucose** (a type of sugar).
Glucose is used for **respiration**, where cells release energy.
Plants use **sunlight** to turn **carbon dioxide** and **water** into **glucose** and **oxygen**.
Word equation: **carbon dioxide + water → glucose + oxygen**.

Where Does Photosynthesis Happen?

Photosynthesis occurs in **chloroplasts**, which contain the green pigment **chlorophyll**.
Chloroplasts are an **organelle** found mainly in leaf **palisade cells**.
Palisade cells are near the top of a leaf to get the most light.
Leaves are adapted with a **large surface area** for photosynthesis.

How Does Carbon Dioxide Enter the Leaf?

Carbon dioxide enters the underside of a leaf through **stomata**.
The **spongy mesophyll** layer has loosely arranged cells with **air spaces**.
Air spaces allow carbon dioxide to **diffuse** through the leaf to palisade cells.

Factors Affecting the Rate of Photosynthesis

The rate is affected by **light intensity**, **carbon dioxide concentration**, **temperature**, and **water availability**.
An experiment can measure the rate using **pondweed** in water.
Cover pondweed with an inverted funnel and place a water-filled test tube over it to capture **oxygen**.
Count oxygen bubbles released in one minute to estimate the rate.
Adjust variables like light intensity or temperature to observe effects.

Internal structure of a leaf showing palisade and spongy mesophyll, stomata, and air spaces.

Chloroplast structure: envelope, stroma, grana, thylakoids, lamellae, and starch grain.

Slides

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Practice questions

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1.Photosynthesis is a chemical reaction that produces which type of sugar?
Easy
- AGlucose
- BSucrose
- CFructose
- DStarch
2.Which of the following statements about photosynthesis is true?
Easy
- APhotosynthesis occurs in mitochondria.
- BPhotosynthesis produces carbon dioxide and water.
- CPhotosynthesis is a chemical reaction that produces glucose.
- DPlants do not carry out respiration.
3.Where does photosynthesis occur in plant cells?
Easy
- ANucleus
- BChloroplast
- CMitochondrion
- DVacuole
4.What are the products of photosynthesis?
Easy
- AGlucose and oxygen
- BCarbon dioxide and water
- CGlucose and carbon dioxide
- DOxygen and water
5.Which leaf cells contain the most chloroplasts and are located near the top of the leaf?
Medium
- ASpongy mesophyll cells
- BPalisade cells
- CGuard cells
- DEpidermal cells
6.What is the function of the air spaces in the spongy mesophyll layer?
Medium
- AThey allow carbon dioxide to diffuse through the leaf to the palisade cells.
- BThey store water for the leaf.
- CThey provide structural support to the leaf.
- DThey absorb light for photosynthesis.
7.In an experiment using pondweed to measure the rate of photosynthesis, what is collected to estimate the rate?
Medium
- ACarbon dioxide bubbles
- BOxygen bubbles
- CGlucose produced
- DChlorophyll released
8.Which of the following is NOT a factor that affects the rate of photosynthesis according to the source?
Medium
- ALight intensity
- BCarbon dioxide concentration
- CSoil pH
- DTemperature

More questions

9.Euglena is a unicellular organism that carries out photosynthesis. Which organelle must it contain?
Hard
- AChloroplast
- BMitochondrion
- CNucleus
- DRibosome
10.How does carbon dioxide enter the leaf?
Hard
- AThrough the cuticle
- BThrough stomata on the underside of the leaf
- CThrough the palisade cells directly
- DThrough the root hairs
11.What is the advantage of palisade cells being located near the top of a leaf?
Hard
- AThey are closer to the stomata for gas exchange.
- BThey receive more light for photosynthesis.
- CThey are protected from herbivores.
- DThey can store more water.
12.In the pondweed experiment to measure the effect of light intensity, which variable should be changed?
Hard
- AThe distance of the lamp from the pondweed
- BThe temperature of the water
- CThe concentration of carbon dioxide in the water
- DThe type of pondweed used
13.In an experiment using pondweed, a student counts 20 bubbles of oxygen released in one minute at a light intensity of 40 units. When the light intensity is increased to 80 units, 35 bubbles are released in one minute. What is the percentage increase in the rate of photosynthesis?
Medium
- A75%
- B57%
- C43%
- D15%
14.A student uses pondweed to investigate the effect of carbon dioxide concentration on the rate of photosynthesis. They add sodium hydrogen carbonate to the water to increase carbon dioxide concentration. Which of the following is the most appropriate way to measure the rate of photosynthesis in this experiment?
Hard
- ACount the number of oxygen bubbles produced per minute
- BMeasure the volume of carbon dioxide consumed per minute
- CMeasure the change in mass of the pondweed per hour
- DCount the number of leaves produced per day
15.The graph shows the rate of photosynthesis at different light intensities for a plant. At point X, the rate stops increasing despite higher light intensity. What is the most likely limiting factor at point X?
Medium
- ACarbon dioxide concentration
- BTemperature
- CLight intensity
- DWater availability
16.A plant is kept in a sealed container with a carbon dioxide sensor. The plant is placed in bright light. Which of the following graphs best shows how the carbon dioxide concentration changes over time?
Medium
- AA downward curve that flattens out
- BAn upward curve that flattens out
- CA straight horizontal line
- DA straight line decreasing at constant rate
17.Which of the following is the correct word equation for photosynthesis?
Easy
- Acarbon dioxide + water → glucose + oxygen
- Bglucose + oxygen → carbon dioxide + water
- Ccarbon dioxide + glucose → water + oxygen
- Dwater + oxygen → glucose + carbon dioxide
18.A student sets up three test tubes of pondweed: Tube A at 10°C, Tube B at 25°C, Tube C at 40°C. All other conditions are the same. After 10 minutes, the number of oxygen bubbles counted is: A=5, B=20, C=8. What conclusion can be drawn?
Hard
- AThe optimum temperature for photosynthesis in pondweed is around 25°C
- BPhotosynthesis stops at 40°C
- CTemperature has no effect on photosynthesis
- DThe rate of photosynthesis increases continuously with temperature
19.In a pondweed experiment, a student uses a lamp at different distances to vary light intensity. At 10 cm distance, 30 bubbles per minute are counted. At 20 cm, 15 bubbles per minute. At 30 cm, 7 bubbles per minute. What is the relationship between light intensity and rate of photosynthesis?
Medium
- AAs distance increases, rate decreases
- BAs distance increases, rate increases
- CThere is no relationship
- DRate is constant at all distances
20.Which of the following is a product of photosynthesis?
Easy
- AOxygen
- BCarbon dioxide
- CWater
- DChlorophyll
21.The diagram shows a cross-section of a leaf. Which layer contains the most chloroplasts?
Medium
- APalisade mesophyll
- BSpongy mesophyll
- CUpper epidermis
- DLower epidermis
22.In the chloroplast diagram, what is the name of the fluid-filled space where the Calvin cycle occurs?
Medium
- AStroma
- BGrana
- CThylakoid
- DLumen
23.A student investigates the effect of light intensity on photosynthesis using pondweed. They use a lamp and change its distance from the pondweed. Which of the following should they keep constant?
Hard
- ATemperature of water
- BDistance of lamp
- CNumber of bubbles
- DTime of day
24.A plant is placed in a sealed transparent container with a light source. The carbon dioxide concentration inside is measured over time. Initially, the concentration is 0.04%. After 2 hours, it is 0.02%. What is the average rate of carbon dioxide uptake per hour?
Medium
- A0.01% per hour
- B0.02% per hour
- C0.03% per hour
- D0.04% per hour
25.In the pondweed experiment described, which apparatus is used to collect the oxygen produced?
Medium
- AA water-filled test tube placed over an inverted funnel covering the pondweed
- BA gas syringe connected directly to the pondweed
- CA balloon tied over the top of the beaker
- DA measuring cylinder inverted over the pondweed without a funnel
26.A student wants to investigate the effect of light intensity on the rate of photosynthesis using pondweed. Which variable should they change?
Medium
- AThe distance of the lamp from the pondweed
- BThe temperature of the water
- CThe concentration of carbon dioxide in the water
- DThe number of pondweed shoots
27.In a pondweed experiment, a student counts 20 bubbles of oxygen per minute at a light intensity of 40 arbitrary units. When the light intensity is increased to 80 units, the bubble count rises to 35 per minute. What is the most likely explanation for the rate not doubling?
Hard
- AAnother factor, such as carbon dioxide concentration or temperature, is limiting the rate
- BThe pondweed has run out of water
- CThe student miscounted the bubbles
- DPhotosynthesis cannot occur at high light intensities
28.Which of the following is a correct method to vary carbon dioxide concentration in a pondweed experiment?
Medium
- AAdd different amounts of sodium hydrogen carbonate to the water
- BUse a lamp at different distances
- CChange the temperature of the water bath
- DUse pondweed of different sizes
29.What is the role of chlorophyll in photosynthesis?
Easy
- AIt absorbs light energy for the reaction
- BIt produces carbon dioxide
- CIt stores glucose
- DIt allows water to enter the leaf
30.A student sets up three test tubes of pondweed: Tube A at 10°C, Tube B at 25°C, Tube C at 40°C. All other conditions are the same. After 10 minutes, the number of oxygen bubbles is recorded. Which tube is expected to have the highest bubble count?
Hard
- ATube B at 25°C
- BTube A at 10°C
- CTube C at 40°C
- DAll tubes will have the same number
31.Which gas enters the leaf through stomata for photosynthesis?
Easy
- ACarbon dioxide
- BOxygen
- CNitrogen
- DWater vapour
32.Why do leaves have a large surface area?
Medium
- ATo absorb more light for photosynthesis
- BTo reduce water loss
- CTo store more glucose
- DTo protect the leaf from insects
33.A plant is kept in a sealed transparent container with a light source. The carbon dioxide concentration inside is measured over time. Initially, the concentration decreases, then levels off. What does the leveling off indicate?
Hard
- AThe rate of photosynthesis equals the rate of respiration
- BThe plant has stopped photosynthesising
- CAll carbon dioxide has been used up
- DThe light source has been turned off
34.In the leaf cross-section, which layer contains loosely arranged cells with air spaces to allow gas movement?
Medium
- ASpongy mesophyll
- BPalisade mesophyll
- CUpper epidermis
- DLower epidermis
35.The diagram shows a chloroplast. Which part is the site of the light-dependent reactions?
Hard
- AThe thylakoid membranes (grana)
- BThe stroma
- CThe outer membrane
- DThe starch grain
36.Which of the following statements is true?
Easy
- APhotosynthesis is a chemical reaction that produces glucose.
- BPhotosynthesis occurs in mitochondria.
- CPlants do not carry out respiration.
- DPalisade cells contain few chloroplasts.
37.Which organelle must a unicellular organism contain to carry out photosynthesis?
Medium
- AChloroplast
- BMitochondrion
- CNucleus
- DRibosome
38.Why is it advantageous that palisade cells are found near the top of a leaf?
Medium
- AThey receive the most light for photosynthesis.
- BThey are closer to the stomata for gas exchange.
- CThey are protected from herbivores.
- DThey can store more water.
39.How does carbon dioxide enter the leaf to reach the palisade cells?
Medium
- AThrough stomata and then diffuses through air spaces in the spongy mesophyll.
- BThrough the cuticle and then travels through xylem vessels.
- CThrough root hairs and then moves up the stem.
- DThrough the palisade cells directly from the atmosphere.
40.Which of the following is NOT a factor that affects the rate of photosynthesis?
Easy
- ANumber of leaves on the plant
- BLight intensity
- CCarbon dioxide concentration
- DTemperature

Revision notes

## Photosynthesis Revision Notes ### What is photosynthesis? - A chemical reaction that produces **glucose** (a sugar). - Glucose is used for **respiration** (releasing energy). ### Word equation **carbon dioxide + water → glucose + oxygen** ### Where does it happen? - In **chloroplasts** (organelles containing green pigment **chlorophyll**). - Palisade cells (near top of leaf) have many chloroplasts to catch light. - Leaves have large surface area for maximum light absorption. ### How does CO₂ enter? - Through **stomata** (underside of leaf). - Spongy mesophyll layer has air spaces for gas diffusion to palisade cells. ### Factors affecting rate - Light intensity - Carbon dioxide concentration - Temperature - Water availability ### Measuring rate (pondweed experiment) - Place pondweed in water under an inverted funnel with a water-filled test tube over it. - Count oxygen bubbles released per minute. - Change light intensity by moving lamp closer/further. ### Key points - Products: glucose and oxygen. - Reactants: carbon dioxide and water. - Palisade cells near top get most light (advantage). - CO₂ diffuses through stomata → air spaces → palisade cells.

Photosynthesis: A chemical reaction that produces glucose using sunlight, carbon dioxide, and water.
Glucose: A type of sugar produced by photosynthesis, used for respiration.
Chloroplasts: Organelles containing chlorophyll where photosynthesis occurs.
Chlorophyll: Green pigment in chloroplasts that absorbs sunlight.
Palisade cells: Leaf cells near the top containing many chloroplasts for maximum light absorption.
Stomata: Pores on the underside of leaves through which carbon dioxide enters.
Spongy mesophyll: Layer of loosely arranged cells with air spaces for gas diffusion.
Respiration: Process where cells release energy from glucose.

Flashcards

What is photosynthesis?

Photosynthesis is a chemical reaction that produces glucose (a type of sugar) using sunlight.

What are the reactants of photosynthesis?

Carbon dioxide and water.

What are the products of photosynthesis?

Glucose and oxygen.

Write the word equation for photosynthesis.

carbon dioxide + water → glucose + oxygen

Where does photosynthesis occur?

In chloroplasts, which contain the green pigment chlorophyll.

What is chlorophyll?

A green pigment found in chloroplasts that captures light energy for photosynthesis.

Which leaf cells contain the most chloroplasts?

Palisade cells.

Why are palisade cells found near the top of a leaf?

To get the most light for photosynthesis.

How are leaves adapted for photosynthesis?

They have a large surface area to capture more light.

How does carbon dioxide enter a leaf?

Through stomata on the underside of the leaf.

What is the role of the spongy mesophyll layer?

It contains loosely arranged cells with air spaces that allow carbon dioxide to diffuse to palisade cells.

What factors affect the rate of photosynthesis?

Light intensity, carbon dioxide concentration, temperature, and water availability.

Describe an experiment to measure the rate of photosynthesis using pondweed.

Place pondweed in water under an inverted funnel with a water-filled test tube over it. Count oxygen bubbles released per minute. Use a lamp to vary light intensity.

How can you change light intensity in the pondweed experiment?

Move the lamp closer or farther away from the pondweed.

What is glucose used for in plants?

It is used for respiration, where cells release energy from glucose.

What organelle must a unicellular organism like Euglena contain to carry out photosynthesis?

Chloroplasts.

True or false: Photosynthesis is a chemical reaction.

True.

True or false: Plants do not carry out respiration.

False. Plants carry out respiration to release energy from glucose.

True or false: Photosynthesis occurs in chloroplasts.

True.

True or false: Palisade cells contain many chloroplasts.

True.

Why is it an advantage that palisade cells are near the top of a leaf?

They receive the most light, maximizing photosynthesis.

Describe the movement of carbon dioxide from the air into palisade cells.

Carbon dioxide enters through stomata, diffuses through air spaces in the spongy mesophyll, and reaches palisade cells for photosynthesis.

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