Sectieoverzicht
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Leerlingen moetenAls voltooid aanduiden
Most cells share features such as having a nucleus, a cell membrane, cytoplasm, and mitochondria. Plant cells tend to be larger than animal cells and have a cell wall, a vacuole and most plant cells have chloroplats.
There are differences between cells. Each type of cell has its own job to do. These cells have specific features that allow them to perform their functions effectively.
Cellular differentiation is the process in which a stem cell changes from one type to a differentiated one. Usually, the cell changes to a more specialized type. Differentiation happens multiple times during the development of a multicellular organism as it changes from a simple zygote to a complex system of tissues and cell types. Differentiation continues in adulthood as adult stem cells divide and create fully differentiated daughter cells during tissue repair and during normal cell turnover.
Image: Haileyfournier. CC BY-SA 4.0
Specialised animal cells:
Red blood cells:
Image: Open Learning Initiative. CC BY-NC-SA
Red blood cells carry oxygen around the body. They are well suited to this function because:
- They contain haemoglobin, which carries oxygen molecules.
- They don't have a nucleus, allowing more space to carry oxygen.
- They are a flat disc shape (biconcave) which gives them a large surface area, and the best chance of absorbing as much oxygen as they can.
Nerve cells transmit electrical signals. They are well suited to their function because:
- They are thin and can be more than 1 metre long. This means they can carry messages up and down the body over large distances.
- Nerve cells have branched connections at each end. These join to other nerve cells, allowing them to pass messages around the body.
- They have a fatty (myelin) sheath that surrounds them. The fatty sheath increases the speed at which the message can travel.
A nerve cell is long and insulated with a fatty layer to carry electrical impulses around the body. Image: Emma Harrage. CC BY
Muscle cells:
Image: CK-12 Foundation. CK-12 License - free to use for education purposes.
Muscle cells bring parts of the body closer together. They are well suited to this function because:
Muscle cells are held together in bundles, which pull together to make muscles contract (get shorter and fatter).
There are different types of muscle cell, each perfectly adapted to its function:
Cardiac muscle cells: Cardiac (heart) muscle cells are branched, and they join together to make a net. Cardiac muscle cells contract rhythmically, even outside the body. They never get tired.
Skeletal muscle cells: Skeletal muscle is joined to bones. Its cells contract to make bones move and joints bend.
Smooth muscle cells: Smooth muscle cells make up thin sheets of muscle, such as the stomach lining. They can also be arranged in bundles, or rings, like that in the anus.
Ciliated cells:
Image: Open Stax CC BY 3.0
Ciliated cells are found in the airways. They have tiny hairs on their tops called cilia which beat in a rhythm. These hairs move mucus containing dust and other particles upwards and out of the airways. Ciliated cells are also found in the oviducts. Here the tiny hairs beat to move the egg from the ovaries to the uterus.
Villi:
Image: snow93. Public domain
Villi are structures about one millimetre long in the small and large intestines. Millions of them poke out to absorb digested food and water into the blood. They are well suited to this function because:
- They have a large surface area.
- They have thin walls which are only one cell thick.
- The cells of the lining have tiny hairs to absorb more food and water.
Specialised plant cells:
Root hair cells:
Image: Emma Harrage. CC BY
Roots hold plants in place as they grow and absorb water and minerals from the soil. Roots divide into smaller and smaller branches as they travel into the soil. The outside surface of root is covered with root hair cells, which have tiny 'hairs' which poke into the soil. This massively increases the surface area for the root hair cell to absorb more water and minerals.
Image: wikiwijs. CC BY
Palisade cells:
Image: domdomegg. CCA 4.0
When the Sun shines, photosynthesis in plant cells makes sugar for growth, reproduction, and other life processes. Photosynthesis occurs in a special chemical called chlorophyll, which is found in parts of plant cells called chloroplasts. Palisade cells are the major site of photosynthesis. They are well adapted for this function because:
- they are towards the tops of leaves for maximum light
- they have lots of chloroplasts
Xylem and phloem cells:
Image: OpenStax. CC BY
Xylem cells transport water from the roots to other parts of the plant. Xylem cells run inside stems of plants from their roots to their leaves. Xylem cells die and their ends break down. This allows them to form long tubes to carry water upwards for photosynthesis. They have thick cell walls to provide support to the plant. This holds the leaves up for photosynthesis and the flowers up for reproduction.
Phloem cells transport sugary water from the leaves to the rest of the plant. Phloem cells are often found near to xylem cells in the stem. Unlike xylem cells, phloem cells are alive. They carry sugary water from the leaves to the rest of the plant. Next to the phloem cells are companion cells which have many mitochondria.
Credit: Fuse Schools - Global Education. -
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