B4 revision notes

B4- It's a Green World

Ecology in the local environment

Ecosystem-a physical environment, these can be natural or artificial

Natural ecosystems- have a high biodiversity which coexist together

Artificial ecosystems- designed  and maintained for a particular purpose eg. greenhouse. this has a low biodiversity because weedkillers, fertilisers and pesticides may be used

A habitat-part of physical environment where an animal or plant lives

A community-total number of individuals that live in a certain area

A population-total number of individuals that live in a certain area of the same species

Sampling methods are pooters, sweepnets, pitfall traps and quadrats. You need to take a big enough sample and sample randomly. You can use transect lines along side the quadrats. Kite diagrams show zonation, which is the gradual change in the distribution of species across a habitat.

Photosynthesis

Green plants make their own food using sunlight, carbon dioxide + water = glucose + oxygen. Van helmont and Joseph Priestly helped discover photosythesis. Glucose and starch can be converted into engergy, proteins, starch and cellulose. Glucose is soluble and can be transported around the plant as soluble sugar, but it must be converted into starch to be stored. Photosythesis can be increased by increasing the temp, light intensity and carbon dioxide concentration. Temp is the limiting factor. Plants respire to breakdown glucose glucose to release energy.

Leaves and Photosynthesis

Leaves contain chloropyll, its broad and flat, has a network of vascular bundles, has a thin structure and has stomata (tiny pores). The leaf has four layers: the upper epidermis, the palisade layer, the spongy mesohpyll and the lower epidermis.

Diffusion and Osmosis

Substances move in and out of cell membranes by diffusion. Diffusion is the movement of a substance from a region of high concentration to a region of low concentration. Rate of diffusion can be increased when theres a greater surface area, greater difference between concentrations and the particles have a shorter distance to travel. During the night photosynthesis stops and oxygen diffuses into leaf cells and carbon dioxide diffusion out of leaf cells. The stomata open to increase the rate of diffusion and close to prevent excessive water loss is drought conditions.

Osmosis is the diffusion of water from high concentration of water (dilute solution) to low concentration of water through a partially-permeable membrane.The net movement of molecules is from the area of high water concentration to the area of low water concentration, this gradually dilutes the solution. Animal cells, unlike plant cells, don't have an inelastic cell wall. Having a inelastic cell wall prevents cells from bursting due to excessive water and contributes to rigidity.

As water moves into plant cells by osmosis, the pressure inside the cell increases. The cell becomes very turgid (rigid) this allows the cells to be upright and firm. However if water is in short supply the plant will become flaccid and the plant will begin to wilt. When cells lose a lot of water the cell will contract, this is called plasmolysis.

Transport in Plants

Xylem…