Nutrition is taking in useful substances. You may recall that nutrition is one of the characteristic of a living thing and therefore it is important that living things take in useful substances ideal for their growth using nutrition.
The process by which plants manufacture carbohydrates from raw materials using energy from light is called as photosynthesis. Photosynthesis is extremely important in the plant’s nutrition.
Chlorophyll- the plant power station
Chlorophyll is a green pigment that is inside a chloroplast molecule.
When the sun shines on a chlorophyll molecule:
- Some of the energy in the light is absorbed by it
- The chlorophyll molecule then releases the trapped energy
- The released energy makes carbon combine with water
- This is done with the help of enzymes in the chloroplast
- This causes glucose to be made
- The glucose contains energy from the light
- Thus the light energy is converted into chemical energy in photosynthesis.
The equation for photosynthesis
Leaves- the plant nutritionists
A leaf contains palisade cells, which contains chloroplasts, which contain chlorophyll molecules, which contain the enzymes that catalyse photosynthesis! Marvellous right?
Let’s learn about the leaf structure now:
|The transverse structure of a leaf|
E Don’t contain chloroplasts
|To protect inner layers of cells
To secrete a waxy substance called the cuticle that covers the upper epidermis.
The cuticle helps in lowering transpiration rates
E Contain small openings called stomata
|To protect inner layers of cells
To help in the gas exchange by using stomata
E Contain chloroplasts
|Control the movement of substances in and out of the stomata|
|Palisade mesophyll cells
E These cells contain many chloroplasts as compared to other plant cells
|To carry out photosynthesis|
|Spongy mesophyll cells||To carry out photosynthesis|
|Air spaces||To help in the diffusion of oxygen and carbon dioxide|
|Xylem tube||To carry water to the mesophyll cells|
|Phloem tube||To take away substances such as sucrose, that the leaf has made|
|Adaptation||Why is it essential?|
|Supported by stem and petiole||To expose most of the leaf to the maximum amount of sunlight and air|
|Large surface area||To expose the cells to the largest amount of sunlight as possible|
|Thin layered||To allow sunlight reach all cells
To allow CO2 to diffuse in
To allow O2 to diffuse out
|Palisade cells are arranged end on (vertically)||To keep as few cell walls as possible between sunlight and the chloroplasts|
|Chloroplasts arranged broadside on (horizontally)||To expose maximum amount of chlorophyll to sunlight|
|Chlorophyll present in cells in the mesophyll layer||To absorb energy from sunlight
So that carbon dioxide combines with water
|No chloroplasts in epidermal layer||To allow sunlight to reach the cells in the mesophyll layer|
|Stomata in lower epidermis||To allow CO2 to diffuse in
To allow O2 to diffuse out
|Air spaces in spongy mesophyll||To allow CO2 and O2 to diffuse in and out of the cells during photosynthesis|
|Chlorophyll arranged on flat membranes inside chloroplasts||To expose maximum amount of chlorophyll to sunlight|
|Xylem vessels within short proximity of mesophyll cells||To supply water to the mesophyll cells for photosynthesis and other functions|
|Phloem vessels within short proximity of mesophyll cells||To carry away sucrose and other organic products of photosynthesis|
Uses of glucose in the plant’s nutrition
|Used for energy||Energy can be released from glucose using aerobic respiration.|
|Stored as starch
(and not as glucose as:
|Stored as starch because:
|Used to make proteins||Nitrate molecules are mixed with glucose to form strands of amino acids which are bound into proteins|
|Used to make organic substances||Organic substances such as:
|Transformed to sucrose for transport||Why sucrose is changed for transport:
Mineral ions required by plants
|To build proteins||Weak growth
|Magnesium||Magnesium ions||To make chlorophyll||E Yellowing between veins of the leaves|
A limiting factor is something present in the environment in such short supply that it restricts life processes. This means that nutrition is restricted at a certain level and the plant is at it’s peak of growth!
Here is a list of some limiting factors you need to know:
|Sunlight||As light intensity increases, the rate of photosynthesis will increase as well
But at a certain point, even if the light gets brighter, the rate of photosynthesis will not increase.
|Carbon dioxide||Similarly, the more the carbon dioxide concentration increases, the more the photosynthesis rate, until a maximum is reached.|
|Temperature||A plant photosynthesises at a greater rate when temperatures are warmer, than colder temperatures|
|Stomata||If stomata are closed, then photosynthesis cannot take place
On a warm, sunny day, stomata often close to decrease transpiration rates.
Hence this can lead to low photosynthetic rates.
Glasshouses- the tools to maximise nutrition
Plants can be grown in glasshouses where environmental conditions can be controlled and hence the plant’s nutrition can be enhanced.
These environmental conditions include:
- Carbon dioxide concentration
- Soil pH
- Moisture (and water)
A range of light intensities can be provided at the correct wavelengths to the plant even in cloudy and dark conditions.
The temperature of the glasshouse can be controlled with heating and cooling equipments, so that the plant gets an optimum temperature to photosynthesise
Carbon dioxide concentration
As the natural carbon dioxide concentration is very low (0.04%) plants cannot photosynthesise at greater rates; whereas, in a glasshouse, it is possible to control carbon dioxide concentrations.
Importance of photosynthesis
- Brings the energy of sun into ecosystems
- Essential for maintaining a constant global level of oxygen and carbon dioxide
- Helps to stop level of carbon dioxide to rise too high
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