Organisation in plants

• What are the factors that effects the rate of transpiration?

  Temperature - higher temp increases rate as water evaporates faster

  Humidity - lower humidity increases rate as the drier the air, the steeper the concentration gradient of water molecules between the air and the leaf

  Wind speed - more wind increases rate as wind removes water vapour quicker, maintaining a steep concentration gradient

  Light intensity - higher light intensity increases rate as the stomata opens wider to let more carbon dioxide into the leaf for photosynthesis
• Root hair cells increase absorption of water and mineral ions into the root by increasing the roof of surface area. They also contain lots of mitochondria to transfer energy, which is used to take in mineral ions by active transport
• Three adaptations of the xylem include them being made of dead cells, no end walk between cells, walls strengthened by a chemical called lignin to withstand the pressure of water
• Leaves are organs as they contain many tissues that work together to perform photosynthesis
• The leaf is made firstly of the waxy cuticle (makes the leaf waterproof), then the upper epidermis (a single layer of cells, protects against water loss, transparent to allow light to pass through it), palisade mesophyll (tightly packed cells, lots of chloroplasts to absorb light for photosynthesis), the sponges mesophyll (spherical cells, lots of air spaces to allow gases to diffuse quickly, large surface area to volume ratio to increase gas exchange), the lower epidermis, then the guard cells (control the opening and closing of the stomata) and the stomata (tiny openings on the lower surface of the leaf that allow gases to move into and out of the leaf)
• Stomata are found on the underside of the leaf to reduce water loss through evaporation. They control gas exchange by allowing diffusion of carbon dioxide into the plant for photosynthesis and they control water loss by allowing diffusion of oxygen out of the plant
• When a plant has plenty of water, the guard cells become turgid, and the cell wall on the inner surface is very thick, so it cannot stretch as much as the outer surface. So, as the guard cells swell up, they curve away from each other, opening the stomata
• Transpiration is when water is lost through the stomata by evaporation. This pulls water up from the roots through the xylem and is called transpiration. The constant movement of water up the plant is called the transpiration steam. It provides water to keep the cell turgid, provides water to cells for photosynthesis and transports mineral ions to leaves
• Translocation is the movement of dissolved sugars from the leaves to the rest of the plant through the phloem. It moves dissolved sugars made in the leaves during photosynthesis to other parts of the plant, which allows for respiration, growth and glucose storage