2. Photosynthesis
2. Photosynthesis
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Define and explain the process of photosynthesis
Define and explain the process of photosynthesis
Hey there, curious minds! 🌱 Get ready to uncover the incredible magic of photosynthesis – the secret process that gives plants their superpowers to create energy and oxygen. Ever wondered how we get fresh air to breathe and delicious food to eat? It's all thanks to photosynthesis! Let's dig in and discover why this amazing natural phenomenon is vital for life on Earth. 🌍
The process in which plants use sunlight, water and carbon dioxide(CO2) to produce oxygen(O2) and energy in the form of sugar (glucose) is called photosynthesis 1.
Fig. 2.1 The Process of Photosynthesis
In the word "photosynthesis" , photo means light and synthesis means to create.
Plants use light energy to manufacture, or create, their own food and hence are called autotrophs.
When a plant is placed in soil, watered, or left outside in the sun, many people mistakenly believe they are "feeding" it, although none of these actions are regarded as food. Instead, plants create glucose, a type of sugar they need to survive, using sunlight, water, and carbon dioxide from the air2. Excess glucose is stored as starch.
Try this activity to check your understanding:
Plants require three elements for photosynthesis to occur: carbon dioxide, water, and sunlight2.
Fig. 2.2 Three elements of photosynthesis
Let's look at the process through which plants receive them3.
The leaves contain a green chemical called chlorophyll, responsible for the green colour of the leaves.
The role of chlorophyll is to absorb energy from sunlight.
When sunlight shines on the leaves, chlorophyll captures the energy from the sun.
Vid. 2.3 Chlorophyll in leaves as seen under high power microscope
Plants have small pores, mostly on the underside of their leaves, that can open and close. These pores are called stomata.
Plants exchange gases through stomata.
Carbon dioxide is a gas in the air. Plants take in carbon dioxide from the air through the stomata.
Fig. 2.4 Exchange of Gases Through Stomata
Watch this video5 to see stomata in action:
Vid. 2.1 Opening and Closing of Stomata
The roots of the plant absorb water from the soil. The water then travels through the stem to the leaves.
Fig. 2.5 Water for Photosynthesis
The process of photosynthesis can be written as:
Watch this video6 to recap your learning:
Vid. 2.2 The Process of Photosynthesis
Complete the process of photosynthesis in this activity:
a. Starch Test7
Testing a leaf for starch is the simplest way to confirm whether photosynthesis has occurred.
To check for the presence of starch in leaves, an iodine solution is used.
A plant leaf is heated for 30 seconds in boiling water, which kills the leaf and stops all chemical activity.
The leaf is placed in a water bath with boiling ethanol for a few minutes (the boiling ethanol dissolves the chlorophyll and turns the leaf colourless).
The leaf is spread on a white tile after being washed with water to rehydrate and soften it.
Use a dropping pipette to add iodine solution.
Fig. 2.6 Starch Test
Watch this video9 to see the experiment:
Vid 2.3 Starch Test on Leaf
Does the entire leaf blade of a variegated leaf photosynthesise starch?
Fig. 2.7 Variegated Leaves
A leaf that has more than one colour is called a variegated leaf. Green regions of variegated leaves have chlorophyll and white portions do not. Iodine solution causes only those areas that were green to turn blue or black, demonstrating the crucial role of chlorophyll in photosynthesis. Because the sections without chlorophyll cannot photosynthesise, they cannot produce starch or change the colour of the iodine.
Glossary
autotrophs: living things that can make their own food using sunlight, water, and carbon dioxide.
glucose: a simple sugar made by plants during photosynthesis. It gives plants energy.
starch: substance made from extra glucose and stored in different parts of the plant for later use.
ethanol: a type of alcohol used in science experiments to remove color (chlorophyll) from leaves.
iodine solution: a liquid used in science to test for starch in plant leaves. It turns blue-black if starch is present.
variegated leaf: a leaf that has two or more colors, usually green and white, showing different amounts of chlorophyll.
Summary
Photosynthesis is the process by which plants use sunlight, water, and carbon dioxide to produce oxygen and glucose (sugar).
Plants are autotrophs, as they create their own food using light energy.
The three elements required for photosynthesis are carbon dioxide, water, and sunlight.
Chlorophyll in chloroplasts traps energy from sunlight.
Carbon dioxide is taken in through small pores called stomata mostly present on the underside of leaves.
Water is absorbed from the soil by the plant's roots and transported to the leaves through the stem.
During photosynthesis, glucose is produced, which provides energy to the plant.
Some glucose is used immediately for plant activities, while the excess is stored in various parts of the plant.
Oxygen is released as a byproduct of photosynthesis and is vital for animals, including humans, to breathe and survive.
References
1 Photosynthesis. National Geographic, n.d, link
2 What is Photosynthesis? Smithsonian, n.d, link
3 Important Factors in Photosynthesis. Super Prof Resources, n.d, link
4 Photosynthesis. Olympiad genius, n.d, link
5 Microscopic footage of the stomata of a plant leaf opening and closing speed up 140. Youtube, n.d, link
6 Photosynthesis. Youtube, n.d, link
7 Photosynthesis. BBC Bitesize, n.d, link
8 Testing a Leaf for Starch. Brilliant Biology Student, n.d, link
9 SHPS test for starch in leaf. Youtube, n.d, link
10 Plant Physiology. NCERT, n.d, link
11 Environmental factors affecting plant growth. Oregon State University, n.d, link
12 How do red leaves photosynthesize? – lack of chlorophyll is a myth. London Middlesex Master Gardeners. (n.d), link
Extensions
Read through the link11 to know the role of light of different wavelengths in photosynthesis: link
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