ICSE Class 10 Biology Chapter 06 Photosynthesis

Are you looking for the ICSE Class 10 Biology book PDF free download. You have come to the right place as we have provided the PDF for Chapter 6 Photosynthesis here. You can refer to the link below to download the ICSE Class 10 Biology Book in PDF Chapter 6 Photosynthesis which is highly recommended textbook for students following the ICSE syllabus for this year. This book has been published by Selina Concise for this academic year and covers important concepts in a detailed manner. Students of ICSE Class 10 will be easily able to understand all concepts and will help students to build a strong foundation in the subject. One of the key chapters in this book is Chapter 6 Photosynthesis which explains all the important topics in lot of detail. The Biology book for Class 10 follows the latest ICSE syllabus for the current year thus ensuring that students get updated with the most relevant content for their studies. By downloading the Selina Concise Biology Class 10 Textbook PDF, students can conveniently access the book anytime and study without needing a physical copy.

Syllabus

Photosynthesis: the nature of the process itself and the great importance of photosynthesis to life in general; experiments to show the necessity of light, carbon dioxide & chlorophyll and also the formation of starch and the output of oxygen; carbon cycle.

Scope Of Syllabus

The internal structure of chloroplast should be explained to give an idea of the site of light and dark reaction. Opening and closing of stomata should be explained. Teachers should stress upon the importance of a correct balanced chemical equation. The terms "photochemical" for light phase and "biosynthetic" for dark phase must be introduced. In the light reaction, activation of chlorophyll molecule followed by photolysis, release of O₂, formation of ATP and NADPH should be taught. In the dark reaction (detailed equations are not required), only combination of hydrogen released by $NADP$ with CO₂ to form glucose to be discussed. Adaptations in a plant for photosynthesis and experiments with regard to the factors essential for the process should be discussed.

Photosynthesis, in a way, is the most significant life process - it provides food for all animal life including humans, and also the life supporting free oxygen gas in the atmosphere for breathing. A whole series of experiments on photosynthesis are worth performing. Hopefully, you will be able to see them through demonstrations.

6.1 Plants - Self Food Producers

All living organisms need food. Animals obtain food from plants but plants prepare it for themselves by the process of photosynthesis.

6.2 What Is Photosynthesis?

Photosynthesis is an important activity of all green plants which are able to synthesise food from carbon dioxide and water in the presence of chlorophyll and light energy. The essential chemical steps in this process are the same in all green plants.

Importance Of Photosynthesis

(1) Food for all. Photosynthesis is ultimately the source of energy and food for all living beings-directly for plants and indirectly for animals and humans who eat the plants or the plant-eating animals.

(2) Oxygen to breathe in. Photosynthesis is the only biological process which releases oxygen into the atmosphere. The oxygen supports all life on the earth.

6.3 Chlorophyll - The Vital Plant Pigment

Chlorophyll (chloro: green, phyll: leaf) is the green colouring matter found in plants. It is contained in microscopic cell organelles called chloroplasts.

Chloroplasts are minute oval bodies bounded by a double membrane, and their interior contains closely packed flattened sacs (thylakoids) arranged in piles (grana) lying in a colourless ground substance called stroma. Ordinarily, there may be 40-50 chloroplasts in a cell. The pigment chlorophyll is contained in the walls of thylakoids. It is a highly complex substance, composed of carbon, hydrogen, oxygen, nitrogen and magnesium. Chloroplasts are mainly contained in the mesophyll cells located between the upper epidermis and the lower epidermis (i.e. in palisade cells and spongy cells) of leaves. These are also found in the guard cells of stomata and in the outer layers of young green stems.

There may be more than 500,000 chloroplasts per sq. mm. of leaf surface.

You will be surprised to know that there are nine types of chlorophyll. Two out of these, chlorophyll-a and chlorophyll-b, are best known and most abundant.

Too Much Light Destroys Chlorophyll

Chlorophyll is highly sensitive to light, so too much light may destroy it. However, the formation of chlorophyll itself depends on the exposure of the plant to light. The grass growing in the shade under a stone turns yellowish due to the non-formation of new chlorophyll and due to the disintegration of the older one in the absence of light.

6.4 Regulation Of Stomatal Opening For Letting In CO₂

Stomata are minute openings occurring in large numbers on the lower surface of a leaf. The main function of the stomata is to let in CO₂ from the atmosphere for photosynthesis. When stomata are not in use for photosynthesis, i.e. when it is dark, they tend to close their openings so that water loss is minimised from the leaves through transpiration. When there is light, as after sunrise, they reopen to allow CO₂ to diffuse in. Transpiration occurs along with photosynthesis. Due to this process, one can say that transpiration is the price which the plant pays for photosynthesis.

The closing and opening of the stomata are on account of the movement of water in and out of the guard cells. They have a thick inner wall facing the opening and a thin outer wall on the opposite side; their cytoplasm contains chloroplasts.

Opening And Closing Of Stomata

There are two theories about the opening and closing of stomata.

(1) Sugar concentration theory (old)

(2) K⁺ ion concentration theory (recent)

(1) Sugar Concentration Theory:

According to the old sugar concentration theory, during daytime, the guard cells begin photosynthesis and the sugar (glucose) produced during the process increases the osmotic pressure which draws in water from the adjoining cells due to endosmosis. Hence, the guard cells become turgid and bulge outwards due to their thin outer wall, thus widening the stomatal opening lying in between. As the stomata open, the diffusion of gases in and out begins for fulfilling the need for photosynthesis and for allowing transpiration.

Closing of the stomata: If for any reason, the water content of the leaf is falling short, the water is drawn out of the guard cells due to exosmosis making them flaccid. As a result, their inner thick walls straighten to close the stomata.

(2) K⁺ Ion Concentration Theory:

According to the recent K⁺ ion concentration theory, the stomatal opening and closing depend on the generation of potassium ion (K⁺) gradient. During daytime, the chloroplasts in the guard cells photosynthesise which leads to the production of $ATP$. This $ATP$ is used to actively pump the potassium ions of the adjacent cells into the guard cells. Increased K⁺ concentration in the guard cells makes them hypertonic, so, more water from the adjacent cells is drawn in and the cells become more turgid and they move outwards to open out the stomatal pore. Reverse happens at night. The K⁺ ions leak out thus reducing the turgor of guard cells and the stomatal pore closes.

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