Photosynthesis Class 10 ICSE Notes
ICSE Class 10 Biology Chapter 6 Photosynthesis Notes, Summary, Definition, Diagram. Photosynthesis Notes.
- Photosynthesis is the process by which living plant cells containing chlorophyll, produce food substance from CO2 and water by using light energy such as sunlight.
Importance of photosynthesis
- Food for plants and indirectly for animals and humans who eat plant
- Oxygen to breathe
Chlorophyll – the vital plant pigment
- It is a green pigment found in plants.
- Highly complex substance composed of carbon, hydrogen, oxygen, nitrogen and magnesium.
- Found inside chloroplast.
- Chloroplasts are minute oval bodies bounded by double membrane which contains thalakoids (flattened sacs), granum (pile of thylakoids), fret (interconnecting bars) and stroma (colourless ground fluid)).
- 30-40 chloroplast present in a cell.
- Chloroplasts mainly present in mesophyll cells located in between upper epidermis (palisade cells) and lower epidermis (spongy cells) of leaves.
- They are also found in guard cells of stomata and outer layers of young green stems.
- Chlorophyll is contained in walls of thylakoids
- Nine types of chlorophyll present. Chlorophyll-a and Chlorophyll-b most abundant.
- Chlorophyll is highly sensitive to light
- Formation of chlorophyll depends on exposure of light to plant.
Regulation of stomatal opening for letting in CO2
- Stomata help in exchange of gases
- When there is no sunlight, they close their opening so water loss can be minimised from transpiration.
- When there is sunlight, they reopen to allow CO2 to diffuse in.
- The opening and closing are on account of movement of water in and out of guard cells.
- They have thick inner wall for opening and thin outer wall on opposite side.
Opening and closing of stomata
- K+ ion concentration theory :
- During daytime, chloroplast in guard cells photosynthesises which leads to the production of ATP.
- ATP is used to actively pump the potassium ions of the adjacent cells into the guard cells.
- Increased K+ concentration makes hypertonic, more water from adjacent cells is drawn in and cells become more turgid and they move outwards to open out the stomatal pore.
- Decreased K+ concentration make hypotonic, K+ ions leak out thus reducing the tugor of guard cells and stomatal pore closes.
- Sugar concentration theory :
- During daytime, during photosynthesis the sugar (glucose) increases the osmotic pressure which draws in water from adjoining cells due to endosmosis. Hence, the guard cells become turgid and bulge outwards due to thin outer wall.
- If 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.
Process of photosynthesis
- During daytime, when sunlight falls on the leaf, the light energy is trapped by the chlorophyll of the upper layer of mesophyll, especially the palisade cells.
- This energy is utilized in chemical processes involved is the manufacture of food, where the raw materials used are CO2 and water.
- CO2 from atmosphere enters the leaf by diffusion down a concentration through the stomata.
- Water from soil taken to stem to leaves
Chemical equation to represent –
6CO2 +12H2O →light energy /chlorophyll→C6H12O6 + 6H2O+6O2↑
Glucose molecule – C6H12O6 is simple sugar readily soluble in water.
6 molecules ofH2O liberated at the end of the process are those that are re-formed during a chain reaction
Two main phase of photosynthesis –
a) Light –Dependent Phase (photo-chemical phase) –
- Light plays the key role
- Light reaction takes place in thylakoids of chloroplasts.
- Activation of chlorophyll – on exposure to light chlorophyll becomes activated by absorbing photons.
- Splitting of water-
2H2O →energy of 4 photons→4H+ + 4e- + O2
- Photolysis – splitting by light , occurs in grana of chloroplast is defined as splitting of H2O molecules into hydrogen ions and oxygen in the presence of light.
End result of the products of photolysis
1.) H+ ion – are picked up by NADP to form NADPH
NADP+ + e- + H+ →enzyme→NADPH
2.) Oxygen – 2O→O2
3.) e- → used to convert ADP into ATP by adding inorganic phosphate
ADP + Pi→ATP
Phosphorylation – addition of phosphate
Photophosphorylation – energy used in the process comes from light
b) Light-independent (dark) phase / biosynthetic phase –
- Reactions not dependent on light
Conversion of glucose into starch and other chemical –
- Green plants convert glucose into starch as it is formed during photosynthesis.
- Polymerisation – glucose molecules are tramsformed to produce 1 molecule of starch.
- Some plants change glucose to sucrose or into some oils,etc.
Adaptation in leaf to perform photosynthesis
- Large surface are
- Leaf arrangement – at right angle to the light source to obtain maximum light
- Cuticle and upper epidermis
- Numerous stomata – allow rapid exchange od gases
- Thinness of leaves – rapid transport
- The chloroplasts
- Extensive vein system
End result of the products of photosynthesis-
1) Glucose –
Stored in insoluble starch form
Converted into sucrose
Used in synthesising fats, proteins, etc
Immediately consumed by plant cells
2) Water – produced in the process nay be re-utilized in the continuance of photosynthesis.
3) Oxygen
Utilisation of synthesised food and its translocation –
Translocation- it gets transported to different parts of plants where it may be reconverted into starch for storage to produce energy for various functions in the plant.
Factors affecting photosynthesis –
I.) External factors –
a) Light intensity
b) CO2 concentration
c) Temperature – rise in temperature causes rate of photosynthesis increase
d) Water content
II.) Internal factors –
a) Chlorophyll
b) Protoplasm – dehydration of protoplasm reduces the rate of photosynthesis
c) Structure of leaf
Destarching (removal of starch) – plant whose leaves are free from starch
When leaf is boiled in water the cells dies.
When boiled the leaf in methylated spirit it will become pale white due to removal of chlorophyll and becomes hard and brittle.
When the leaf is dipped in iodine solution, blue-black colour appears due to presence of starch. And the leaf without starch will show brown colour.
Sunlight is required for photosynthesis as when iodine staining done only that part where sunlight reaches shows presence of starch.
Importance of photosynthesis –
1) Provides food
2) Provides oxygen
Carbon cycle –
→ Is a series of chemical reactions in which carbon as chemical element (in CO2) is removed from air used by living organisms in their body process and finally returned to the air.
- Steps in carbon cycle are –
1) Photosynthesis
2) Food chain
3) Respiration
4) Decay – dead remain of plants and animals are consumed by decomposers which break organic matter and release CO2 back to atmosphere.
5) Combustion (burning)
6) Heating limestone
- Food chain –
For more update follow net explanations homepage