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SB2 - Cells and control (SB2h - The eye (Colour blindness (When someone…
SB2 - Cells and control
SB2a - Mitosis
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Interphase = the cell makes extra sub-cellular structures, DNA replicates, the copies of chromosomes stay attached to each other in X shapes
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Anaphase = the chromosome copies are separated and moved to either end of the cell on the spindle fibres
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Cytokinesis = a cell surface membrane forms to separate the two cells (cell walls also form in plant cells)
Asexual reproduction
Produces offspring that are clones, meaning that the cells have the same chromosomes as the parent (genetically identical)
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SB2b - Growth in animals
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Cell differentiation
New cells formed will change in different ways so they become specialised for different functions - differentiation
SB2c - Growth in plants
Meristems are a group of cells near the end of each shoot and root and they allow plants to continue growing throughout their lives
In most plants there is a zone of cell division, zone of elongation, and zone of differentiation
Percentage change in plant growth is calculated using the formula final value - starting value / starting value * 100%
SB2d - Stem cells
Stem cells are cells that can divide repeatedly over a long period of time to produce cells that the differentiate
In plants, stem cells are found in the meristems
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Adult stem cells = cells that can only produce the type of specialised cell that is in the tissue around them
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Embryonic stem cells can also be used to treat diseases such as diabetes (type 1), or to replace damaged cells, by stimulating stem cells to make them produce the specialised cells that are needed and then injecting them into the places they are needed
Sometimes, the stem cells can cause a cancerous tumor in the body
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SB2e - The brain
Cerebral cortex
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Divided into two cerebral hemispheres, the right controlling the left half of the body and vice versa
Responsible for movement, intelligence, memory, language and vision
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Medulla oblongata
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Responsible for reflexes such as vomiting, sneezing and swallowing
Connects the brain to the spinal cord, which consists of many nerves and they carry information between the brain and the rest of the body
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SB2h - The eye
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The lens refracts light, focusing it onto the retina
The retina is the light sensitive part and it's covered in receptor cells called cones and rods which detect light
Rods are more sensitive in dim light, but can't sense colour
Cones are sensitives to different colour, but
The information from light is converted into electrical impulses. The optic nerve carries these impulses from the receptors to the brain
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Colour blindness
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The most common form is red-green colour blindness (when red or green cones in the retina are not working properly
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Cataracts
A cloudy patch on the lens, which stops light from being able to enter the eye normally
People with cataracts are likely to have blurred vision, colours may look less vivid and they may have difficulty seeing in bright light
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