Plant Nutrition

Nutrition

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.

Photosynthesis

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.

Photo:  Light

Synthesis: Manufacturing

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

Word equation:

Chemical equation:

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
Leaf part Function
Epidermis (upper)

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

Epidermis (Lower)

E Contain small openings called stomata

To protect inner layers of cells

To help in the gas exchange by using stomata

Guard cells

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

Use Notes
Used for energy Energy can be released from glucose using aerobic respiration.
Stored as starch

(and not as glucose as:

  •  It is reactive
  •  It is soluble in water
  •  It is a small molecule
  •  It might be lost from plant cells when dissolved in water
  •  It may indulge in unwanted chemical reactions in the cells
  •  It may increase the glucose concentration in the cell and cause damage)
Stored as starch because:

  •  Is a large molecule
  •  Is unreactive
  •  Is not very soluble
  •  Can be turned into small pieces
  •  Can be easily stored inside chloroplasts
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:

  •  Sucrose
  •  Cellulose
  •  Chlorophyll (using nitrogen and magnesium)
  •  Fats
  •  Oils
Transformed to sucrose for transport Why sucrose is changed for transport:

  •  Less reactive
  •  Small molecules
  •  Soluble in sap in phloem vessels

 

Mineral ions required by plants

Mineral ion Element Function Deficiency
Nitrogen Nitrates

OR

Ammonium ions

To build proteins Weak growth

Yellow leaves

Magnesium Magnesium ions To make chlorophyll E Yellowing between veins of the leaves

Limiting Factors

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:

Limiting factor Notes
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:

  • Light
  • Temperature
  • Carbon dioxide concentration
  • Soil pH
  • Moisture (and water)

Light

A range of light intensities can be provided at the correct wavelengths to the plant even in cloudy and dark conditions.

Temperature

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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