How plants and animals are organised (Cells, tissues, organs and organisms)
Levels of organisation Cells
Multicellular animals and plants consist of different types of cells organised in a hierarchy:
Cells are the smallest unit of life. They have different features and functions in an organism. Humans are multicellular, meaning they have many cells. These cells are specialised and work together to keep the organism alive.
Specialised cells and their function Animal cells Red blood cell: have a large cell membrane surface area and are designed to absorbs and carries oxygen across the organism. Sperm cell: Fertilises the egg cell and has a long wiggly tail to facilitate movement. Egg cell: Full of cytoplasm and if fertilised, it develops into an embryo. Plant cells Palisade Leaf cell: Consists of many chloroplasts and carries out photosynthesis. Has a tall shape, which gives it a large surface area for absorbing CO2 from the air in the leaf. Tall shape also increases the chances for light to hit the chloroplasts. Guard cell: Their function is to open and close, facilitating the exchange of gases and water vapour. Have a kidney like shape. The gap or pore in the middle of two guard cells is called a Stoma. Stomata (many pores) opens and closes as the cell becomes turgid or flaccid. They are sensitive to light, opening during day-time and closing at night. Closing during night helps to prevent water losses from the plant. Their thin outer walls and thickened inner walls are ideal for opening and closing function.
Although all cells share common features, they are designed to do a particular job within an organism. The structure of each cell relates to its function.
Nerve cell: carries message around the body and has long thin shape.
Root hair cell: these specialised root cells grow as long thin hairs which spread out into the soil. This enables the plant to have a large cell membrane surface area for absorbing water and mineral salts from the soil.
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