Structure of Plants

• Plants have specialised cells that are adapted to perform different functions.

  For example, palisade mesophyll cells are specialised for photosynthesis. They are specialised because they contain a lot of chloroplasts.
• Specialised cells join together to make tissues.
• Another type of tissue is meristem tissue
• Meristem tissue contains special cells that can turn into any type of plant cell.

  The growing tips of roots and shootscontain meristem tissue.

  Meristem allows the plant to grow.
• palisade mesophyll tissue joins with other tissues to form a leaf.
• Plants have different organs, such as roots, stems and leaves.
• The roots, stems and leaves work together in an organ system.

  This system transports substances around the plant.
• A leaf is an organ containing tissues adapted for photosynthesis
• The epidermal tissue is the outer layer of tissue in the leaf that has a waxy cuticle that protects against water loss.
• Epidermal tissue is also thin and transparent to allow sunlight through.
• Palisade mesophyll tissue and spongy mesophyll tissue are also found in leaves
• Palisade mesophyll cells are tall, thin and tightly packed.

  They have a lot of chloroplasts.

  This helps to increase the amount ofsunlight they absorb.
• The more sunlight the chloroplasts absorb, the more the plant canphotosynthesise.
• Spongy mesophyll cells also contain chloroplasts.

  They also have spaces around them to allow gases to diffuse more quickly.
• The leaf also contains xylem and phloem tissue
• Xylem and phloem both help to support the leaf.
• Xylem cells transport water up the plant
• Phloem cells transport sugars up and down the plant.
• A leaf has pores called stomata. The opening of the guard cells that allow gases, carbon dioxide and oxygen, to enter and exit the leaf by diffusion.
• There are more stomata on the underside of a leaf than the top.
• Each stoma is surrounded by guard cells.When the guard cells are filled with water they swell. This makes the stomata open, and allows gas exchange to happen.
• When there is a shortage of water, the guard cells shrink.

  This closes the stomata, so less water vapour is lost through the pores.
• Transpiration is the loss of water from a plant.
• Transpiration is caused by evaporation and diffusion of water through the stomata.
• Often there is more water in the plant than in the air surrounding it.

  As a result, water leaves through the stomata by diffusion.
• Plants can control the level of gas exchange and water loss by opening and closing the stomata.
• The transpiration rate depends on the conditions surrounding the plant
• Transpiration happens at a faster rate when it is hotter.
• When the air is dry, there are fewer water particles in the air.

  As a result, more water leaves the plant by diffusion in dry conditions