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biology (cells and control (mitosis - cell division, where a cell splits…
biology
cells and control
mitosis - cell division, where a cell splits into 2 daughter cells, which are both identicall to the parent cell.
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Interphase - in this phases cells make extra sub-cellular parts (mitochondria, ribosomes etc.) DNA replication occurs to make replicas of all 46 chromosomes. these copies of chromosomes stay attached to each other making the chromosomes look like Xs.
Prophase - centrioles move to the poles of the cells as the nucleus starts to break down. from the centrioles, spindle fibres, made of microtubules, start to emerge
the nuclei of human body cells contain two copies each of 23 types of chromosome, one from mum and one from dad, making 46 in all. cells with two copies of chromosomes are diploid. gametes (sex cells) contain only one copy and are called haploid.
Cytokinesis - a cell surface membrane forms so the cells can completely separate - if in a plant cell the cell walls will form.
Metaphase - spindle fibres connect the selves to the middle of the X and line up all the pairs of chromosomes along the center of the cell
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Anaphase - the chromosome copies are separated out and they are pulled by the spinel fibres the the poles of the cell, with 46 on each side.
Asexual reproduction - when an organism reproduces with just one parent and the offspring are clones - they are genetically identical (same chromosomes as there parent). asexual reproduction relises of mitosis and is alot faster then sexual reproduction as it does not need other organisums. sexual reproduction produces variation, but asexual reproduction does not.
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some animals such as aphids can also reproduce asexually, but in larger animals it is very rare (exception of female Komodo dragons)
Cancer tumours - normal cells only divide when they need to. however cancer cells undergo uncontrollable cell division when a regular cell has been damaged or changed. this rapid division produces growing lumps of cells known as tumours which can damage the body and result in death.
growth in animals
the growth of human babies are regularly checked by measuring the mass and length, these measurements are compared on charts to compare how well a baby is growing to others of the same age.
these charts where created to by measuring a very large amount of babies and the measurements where divided into 100 different groups. when divided like this we can find out what percentage of readings are below a certain value, or percentile. e.g 25% of babies will have a mass below the 25th percentile line, where as 75% of babies will have a mass below the 75th percentile line.
the curved lines show the rate of growth of a baby, but most babies to grow at the same rate all the time, so plotting their mass helps identify if the baby is growing normally.
Cell differentiation - all animals develop from a single cell, but not all cells are the same. some cells change (specialise) to become adapted to there functions. the process of specialisation is called differentiation
growth in plants
Meristems - group of cells near the end of each shoot and root allows plants to continue growing through out their lives. these cells divied rapididly by mitosis and many then elongate and the differentiate into specialised cells.
many types of specialises cells e.g: xylem cells and rot hair cells. the many types of cells allow the plant to carry out many different functions efficiently
there are many different ways of measuring growth in plants, including height, leaf surface area and mass. percentage changes are often worked out for these values and can be calculated using: ((final value - start value) / starting value) x 100
stem cells - cells that can divide repeatedly over long periods of time into cells that can differentiate. (in plants they are found in the meristem so are called meristem cells)
plant stem cells are usually able to produce any kind of specialised cell through out its life time, however most animals can not, especially vertebrates.
animals start life as a fertilised egg which then mitoses into a embryo. the cells of an early aged embryo are embryonic stem cell that can produce any type specialised cell. As the cell continue to divide the embryo developed different areas that will become different organs. the stem cells in these areas become more limited in what they can specialise into.
by the time you are a adolescent your stem cell only produce the specialised cells in the tissue around them, these are called adult stem cells. the adult stem cells in human tissue are often found in bone marrow and allow tissue to grow or repair damaged cells.
stem cells offer a ways to cure different diseases, caused by damaged cells. since the late 1950's scientists have studied how to use adult and embryonic stem cell in oder to cure diseases like type 1 diabetes or damaged cells. this is done by stimulating stems cells into producing the stem cells that are needed and injecting these into the place where they are needed.
there are problem using stems, for example: they can cause cancer if they continue to dive once they have replaced the damaged cells. also stem cells from one person are often rejected by the person they are put into and killed by the immune system.
the brain
once an embryo is 3 weeks old, the stems cells in the brain area start to differentiate into neurones which make up most of the brain. an adult brain has about 86 billion neurones which are interconnect with one another and the rest of the body to process the information and control the body
cerebral cortex - makes up 80% of the brain and is used for most of our senses, language, behaviour, memory and consciousness (our inner thoughts and feelings). it is divided into two cerebral hemispheres, each with slightly different functions. the right side communicates with the left side of the body and vice versa
modern ideas about its functions started to develop thanks to an American rail way accident in 1848. An American railway worker, Phineus Gage was checking if a stick of dynamite was properly in place, poking it with a long metal poll when the dynamite went off and sent the stick of metal upwards through his head. Remarkably gage was unconscious for only a few moments before being able to walk and talk normally. before the accident he was kind and hardworking, however afterwards he was lazy and bad tempered. this led Gages doctor to conclude that the front of the cerebral cortex is involve in controlling personality.
cerebellum - located at the base of the brain and is divided into 2 halves. it controls balance and posture and also coordinates the timing and fine control of muscle activity, making sure that movements are smooth. many musicians have developed changes in the cerebellum, including an increase in size.
medullar oblongata - controls your heart rate and your breathing rate and is also responsible for your reflexes such as swallowing, sneezing and vomiting. the mass of neurones that make up the medullar oblongata connect the brain to the spinal cord. the spinal chord is about the with of a finger and is made up of many nerves (bundles of neurones). these cary information between the brain and the rest of the body.
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hypothalamus - controls things like thirst, hunger and body temperature and the release of many hormones.
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health, disese and the develpoment of medicin
animal coordination, control and homostasis