Leaf structure:

Cuticle:

  • A waxy layer.
  • It prevents water loss from the leaf surface.
  • It protects the leaf.
  • It is secreted by cells of the upper epidermis

 Upper epidermis:

  • It is thin and transparent – allows light to pass through.
  • Contains no chloroplasts.
  • It protects internal tissues from mechanical damage and bacterial and fungal invasion.

Palisade Mesophyll (layer):

  • It contains many chloroplasts so main region for photosynthesis.
  • Its columnar cells (quite long) closely packed together with lot of chloroplast.
  • It absorbs light more efficiently.
  • This layer receive Carbon dioxide by diffusion from air spaces in the spongy mesophyll.

Spongy Mesophyll (layer):

  • The irregular cells (mostly spherical) are loosely packed together to leave numerous large air spaces in between them.
  • Air spaces are pr between cells allow gaseous exchange – carbon dioxide diffuses in to the cells while oxygen diffuses out of the cells during photosynthesis
  • Some (less than palisade mesophyll) chloroplasts are present for photosynthesis.

Vascular bundle:

· This is a leaf tissue, made up of xylem and phloem(vascular bundles).
· Xylem vessels/tubes bring water and minerals to the leaf from root to upwards. Movement of water in plant is unidirectional.
· Phloem vessels/tubes translocate/transport sugars and amino acids away from leaves to whole plant body and this process is called translocation. Movement of food in plant is bidirectional.

Why does Xylem tubes transport the water in unidirectional?

The transport of water in xylem takes place from roots to  leaves therefore its way is unidirectional. And plants only absorb the water from roots for its requirement.

Why does Phloem tubes transport the sugars and amino acids in bidirectional?

Food is manufactured in leaves and has to be distributed all over the parts of the plants. And above all surplus food also stored sometimes stored in  roots that requires to distribute in whole plant body in future.

Lower epidermis:

  • Its structure is same as upper epidermis except the cuticle is thinner comparatively.
  • It acts as a protective layer or a barrier agaist microbes to enter into the leaf.
  • Mostly Stomata are present under the surface of leaf to regulate the loss of water vapour (transpiration)
  • It is also the site of gaseous exchange into and out of the leaf.

Stoma (plural: stomata):

  • These stomata open during day and closes at night.
  • A pair of bean or kidney shaped guard cells are present around a stoma that control the opening or closing of it.
  • Water vapour passes out during transpiration while Carbon dioxide diffuses in and Oxygen diffuses out during photosynthesis.
  • Evaporation of water also takes place from here.
  • Found in greater concentration in lower epidermis, under the lower surface of leaf.

 

How does photosynthesizing cell obtain carbon dioxide?

 

Pathway of carbon dioxide from atmosphere to chloroplasts by diffusion:

Atmosphere → air spaces around spongy mesophyll tissue → leaf mesophyll cells → chloroplast

 

Why plants need mineral salts?

Plants need minerals for healthy growth. They absorb the minerals through the roots by a process called active transport (energy required for this process) as mineral ions dissolved in the soil water.

Why minerals like Magnesium and nitrate are required for a plant?

Magnesium ions and nitrate ions are needed for the the growth of the plants. A plant does not grow well and stay healthy if it cannot get enough of these mineral ions, and it will show symptoms of mineral deficiency.

 

Mineral ions Needed For Effects of deficiency
Magnesium Making chlorophyll Leaves turn yellow
Nitrate Making amino acids Stunted growth

 

 

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