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Cell structure and function

  • Animal cells have: nucleus (contains DNA-contains instructions for making proteins e.g. enzymes used in photosyntheses) cytoplasm (gel-like substancewhere proteins like enzymes are made- some chemical reactions take place here, e.g. anaerobic respiration) cell membrane (holds cell together and controls what goes in and out, lets gases and water pass through freely whilst being a barrier to other chemicals) Mitochondria (where enzymes needed for aerobic respiration are found and where the reactions take place) 
  • Plants have a few extra things: Rigid cell wall (made of cellulose, supports and strengthens cell) Vacuole (contains cell sap, a weak solution of sugar and salts) Chloroplasts (these are where reactions for photosynthesis take place, contain a green substance called chlorophyll and the enzymes needed for photosynthesis) 
  • Yeast- single celled microorganisms- used to make bread and wine: nucleus, cytoplasm, cell membrane, cell wall, mitochondria. 
  • Bacteria- simple cell structure- no nucleus, they have a circular molecules of DNA which floats in the cytoplasm, don't have mitochondria, but they can still aerobically respire. 
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  • Enzymes are proteins that speed up chemical reactions
  • The instructions for making enzymes are found in a cell's genes
  • Chemical reactions usually involve things splitting or joining, a substrate is a molecule that is changed in a reaction, every enzyme molecule has an active site where a substrate joins on to the enzyme, it has to be the correct shape to fit the active site which is why enzymes tend to only speed up one chemical reaction- "lock and key model"
  • Enzymes need to be at the right temperature, they work at an optimum temperature, but any higher and they'll begin to denature (the bonds in the enzyme are interfered with)
  • Enzymes have an optimum pH, if the pH is too high or low it interferes with the bonds holding the enzyme together, this changes the shape of the active site and denatures the enzyme. 
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Aerobic Respiration

  • Respiration is a series of chemical reactions that release energy by breaking down large food molecules. It happens in every living cell. 

Energy released by repsiration can be used to power some of the chemical reactions that happen in cells:

  • Movement-needed to make muscles contract
  • Active transport- process uses energy to move some substances in and out of cells
  • Synthesis of large molecules- lots of polymers are made my joining molomers together, this requires energy- e.g. glucose is joined together to make things like starch and cellulose in plant cells, in plant cells, animal cells and microorganisms, glucose and nitrogen are joined to make amino acids, AAs are joined to make proteins.

Aerobic=with oxygen

  • it releases more energy per glucose molecule than anaerobic respiration, used more than anaerobic (in humans), takes place in plants, animals and some microorganisms
  • Glucose + oxygen -> carbon dioxide + water  (+energy released) 
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Anaerobic respiration

  • Takes place when there is little/no oxygen available
  • Human cells: when a person does really vigorous exercise the body can't supply enough oxygen to your muscle cells for aerobic respiration, so they anaerobically respiring. 
  • Plant cells: if the soil a plant's growing in becomes waterlogged there'll be no oxygen available for the roots so the root cells will have to respire anaerobically
  • Bacterial cells: bacteria can get into small places with little oxygen, so it does to survive
  • In animal cells and some bacteria, anaerobic respiration produces lactic acid: GLUCOSE-> LACTIC ACID (+ ENERGY RELEASED) 
  • In plant cells and some microorganisms (e.g. yeast) anaerobic respiration produces ethanol and C02: GLUCOSE-> ETHANOL +CARBON DIOXIDE (+ENERGY RELEASED) 
  • Fermentation is when organisms break down sugars into other products as they respire anaerobically, humans use fermentation to make..
  • BIOGAS- a fuel used for heating and lighting, lots of different microogranisms used, they ferment plant and animal waste (containing carbs), biogas they produce is mainly methane and carbon dioxide. 
  • BREAD- the yeast ferment the carbs in flour and release CO2 which causes the bread to rise
  • ALCOHOL- yeast ferment sugar to form alcohol, sugar used in alcohol production comes from things like grapes and barley
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  • Photosynthesis happens in: cells in green parts of plants and some microorganisms
  • chlorophyll is needed for photosynthesis- a green substance which absorbs sunlight and allows the energy to be used to convert carbon dioxide and water into glucose
  • Oxygen is produced as a waste product
  • Organisms that photosynthesise form the start of food chains, they make the energy from the sun available to other organisms by converting iy to glucose, the energy is transferred when the photosynthetic organisms are eaten. 
  • Plants use glucose in three main ways...
  • Respiration- this process releases energy from glucose
  • Making chemicals for growth- glucose is converted into cellulose for making cell walls, glucose is combines with nitrogen to make amino acids, which are then made into proteins. Glucose is also used to help make chlorophyll
  • Stored as starch- turned into starch and stored in roots, stems and leaves- used when rate of respiration is slower 
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Rate of Photosynthesis

  • Three factors effect rate of photosynthesis: LIGHT, TEMPERATURE AND AMOUNT OF CO2. 
  • Any of these can become a limiting factor, which factor is limiting at a particular time depends on environmental conditions: night time, seasons etc. 
  • LIGHT- provides energy needed for photosynthesus, as the light level is raised, rate of photosynthesis increases steadily but only up to a certain point
  • CARBON DIOXIDE- one of the raw materials used in photosynthesis, will only increase rate up to a certain point, then it is no longer the limiting factor
  • TEMPERATURE- too low+ enzymes needed for photosynthesus work more slowly because lack of kinetic energy, but if it gets too hot, enzymes can denature. These enzymes denature at approx. 45 degrees celcius. 
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Investigating Photosynthesis

Transects- a way of investigating something across and area. To set one up you tun a tape measure between two fixed points, then you start at one end and collect the data you want. 

Things that will help you collect data: 

  • Light meter: need to measure the level of light, it's a sensor that accurately measures light level. 
  • Quadrat: to make data collection quicker and easier you can use a quadrat (a sqaure frame grid divided into a hundred smaller squares). You can use this to estimate percentage cover of a species. 
  • Identification key: a series of questions that you can use to figure out what plant is is, narrowing down your options. 
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Diffusion, Osmosis and Active Transport

  • DIFFUSION IS THE PASSIVE OVERALL MOVEMENT OF PARTICLES FROM A REGION OF THEIR HIGHER CONCENTRATION TO A REGION OF THEIR LOWER CONCENTRATION (e.g. when plants photosynthesise they use up CO2 from the atmosphere snd produce O2, these gases pass in and out by diffusion) 
  • A partially permeable membrane is one that only allows certain substnces to diffuse through it, e.g. it may onl allow small molecules like water to pass through it and not larger molecules like sucrose. This concentrated sucrose solution gets more dilute as more water moves in, the water acts like it's trying to even up the concentration either side of the membrane. Plants take in water by osmosis. 
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DNA- Making proteins

  • A DNA molecule has two strands coiled together in the shape of a double helix, each strand is made up of lots of small units called nucleotides.
  • Each nucleotide contains a small molecule called a base- DNA has four different bases-A,T,G,C. The two strands are held together by the bases which always pair up in the same way (A+T and C+G) 
  • a gene is a section of DNA that contains the instructions for one particular protein, cells make proteins by joining amino acids together in a particular order. It's the order of the bases in a gene that tells the cell what order to put the amini acids in. Each set of three bases (a triplet) codes for one amino acid. 
  • Proteins are made in the cell cytoplasm by organelles called ribosomes. DNA can't move out of the nucleus because it is really big, to get the information from the DNA to the ribosome, a copy of DNA is made using a molecule called messenger RNA. mRNA is very similiar to DNA but it is shorter and only a single strand. 
  • This is done by: two DNA strands unzip, a molecule of mRNA is made using one strand of thr DNS as a template, base pairing ensures an exact match. mRNA molecule moves out of the nucleus and joins with a ribosome in the cytoplasm. The ribosome then has to stick amino acids together in a chain to make a protein, folllowing the order of bases in mRNA. 
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Cell Division- Mitosis

Cells of your body divide to produce more cells so your body can grow and replace damaged cells. Cells grow and divide over and over again- the cell cycle. There are two stages..

First: the cell has to copy everything it contains so that when it splits in half the new cells will contain the right amount of material. The number of organelles increases during cell growth and the chromosomes are copied so that the cell has two copies of its DNA. 

Then it splits in two by mitosis: 

  • the cell had two copies of DNA all spread out in long strings
  • before the cell divides, the DNA forms x-shaped chromosomes, each 'arm' of a chromosome is an exact duplicate of the other. 
  • The chromosomes then line up at the centre of the cell and cell fibres pull them apart. The two arms of each chromosome go to opposite ends of the cell. 
  • Membranes from around each of the sets of chromosomes, these become nuclei of the two new cells.
  • Lastly the cytoplasm divides, then you have two new cells containing exactly the same DNA- they're genetically identical to eachother and the parent cell. 
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Cell Division- Meiosis

Gametes have half the usual number of chromosomes because during sexual reproduction, an egg and sperm combine to form a new cell- a zygote. Gametes only have 23 chromosomes (one copy of each), so when the zygote is formed it had 46 chromosomes. 

  • Meiosis involves two divisions, it produces new cells that have only half the original number of chromosomes. In humans it only happens in the ovaries and testes. 
  • As with mitosis, before the cell starts to divide, it duplicates its DNA- one arm of each chromosome is an exact copy of the other arm.
  • FIRST DIVISION: the chromosome pairs line up in the centre of the cells. The pairs are then pulled apart, so each new cell only has one copy of each chromosome. A mix from either parent. 
  • SECOND DIVISION: the chromosomes line up in the centre of the cell, the arms of the chromosomes are pulled apart. 
  • You get four gametes with only a single set of chromosomes in it. 
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Animal Development

  • A fertllised agg (zygote) divides by mitosis to produce the embryo of the new organism. Initially, the cells in the embryo are all the same- they're embryonic stem cells. These are undifferentiated so they are able to divide to produce any type of specialised cell. In humans,  all the cells in the embryo are undifferentiated up to the eight cell stage. The process of stem cells becoming specialised is differentiation. After the eight cell stage, most of the stem cells in the human embryo start to differentiate. The embryo then begins to develop tissues (groups of specialised cells) and organs (groups of tissues). Adult humans only have stem cells in places like in the bone marrow. Adult stem cells become specialised but they aren't as versatile as embryonic stem cells, they can only differentiate into certain kinds of cells. All body cells contain the same genes, but in specialised cells most of the genes are not active, they only produce the proteins they need. Stem cells can switch on any gene during their development- the genes that are active determine the type of cell a stem cell specialises into. 
  • Adult stem cells are already used to cure disease, for examp. people with blood diseases can be treated with bone marrow transplants. Bone marrow contains stem cells that can turn into new blood cells and replace old faulty ones.
  • Embryonic stem cells can be extracted from early embryos, these can then be specialised to replace faulty ones in sick people. To get a specific cell, scientists try control differentiation of the stem cells by altering conditions to activate certain genes. 
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Development continued

  • Embryonic stem cells can be extracted from early embryos, these can then be specialised to replace faulty ones in sick people. To get a specific cell, scientists try control differentiation of the stem cells by altering conditions to activate certain genes.  
  • Cloning can be used to make stem cells...
  • Take an egg cell and remove its genetic material
  • a nucleus from a body cell of the adult you're cloning is then inserted into the 'empty' egg cell. 
  • under the right conditions, inactive genes in the nucleus of the body cell can be reactivated so that the embryo forms
  • Embryonic stem cells can then be extracted from the embryo- these stem cells could then be controlled to form any type of specialised cell 
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Plant Development

  • In plants, the only cells that are mitotically active are found in the plant tissues called meristems. Meristem tissue is found in the areas of a plant that are growing- such as the roots and shoots. Meristems produce unspecialised cells that are able to divide and form any cell type in the plant- they act as embryonic stem cells. These can divide to generate any type of cell for as long as the plant shall live.  The unspecialised cells can become specialised and form tissues like xylem and phloem ( water and food transport tissues) These tissues can group together to form organs like leaves, roots, stems and flowers. 
  • A cutting is part of a plant that has been cut off it, cuttings taken from an area of the plant that's growing will contain unspecialised meristem cells which can differenitate to make any cell. This means a whole new plant can grow from the cutting which will be a clone of the parent plant. Gardeners often take cuttings from plants with desirable characteristics. 
  • Rooting powder helps cuttings to geow into complete plants because it contains plant hormones (auxins)- they'll produce roots rapidly and start growing as new plants. This helps growers to produce lots of clones v quickly. 
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  • Phototropism- growth towards or away from light. 
  • Some parts of a plant can respond to light by growing in a certain direction
  • Shoots are positively phototropic and grow towards light.
  • Roots are negatively phototropic- they grow away from light.
  • Phototropism helps them to survive. 
  • Positive: plants need sunlight for photosynthesis, they need that for energy and growth. Photosynthesis occurs mainly in leaves, so it is important for plant shoots to grow towards light.
  • Plants need nutrients and water from the soil to grow, phototropism means they'll grow away from light, down into the soil where they can absorb the water and nutrients the plant needs. 
  • Auxins are chemicals that control growth near the tips of shoots and roots, they are produced in the tips and diffuse backwards to stimulate cell elongation process (enlargement), which occurs in the cell sjust behind the tips. If the tip is removed, no auxins are available and the shoot may stop growing. Auxins are involved in resposnses of plants to light, gravity and water.
  • Auxins make shoots grow towards the kught, more ausins accumulate on the dark side than the light side so it bends towards the light. 
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The Nervous System

  • The NS detects and reacts to stimuli, it's made of up different parts
  • Central nervous system - in vertebrates this consists of mainly the brain and spinal cord only, but in mammals the CNS is connected to the body by sensory and motor neurones- these make up the peripheral nervous system.
  • Sensory neurones carry impulses from the receptors to the CNS
  • Motor neurones carry impulses from the CNS to effectors
  • Effectors- all your muscles and glands which respond to nervous impulses
  • Receptors-cells that detect stimuli- many different types- taste, sound etc. These can form parts of larger, complex organs e.g. the retina of the eye is covered in light receptor cells
  • Effectors respond to nervous impulses and bring about a change, effectors can also form part of complex organs. There are two types of effector- muscle cells- make up muscles. And hormone secreting cells- found in the glands e.g. cells that secrete the hormone ADH are found in the pituitary gland. 
  • Central Nervous system coordinates a response- the CNS is a processing centre, it recieves info from receptors and then coordinates a response.
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Neurones and Synapses

  • when stimulated neurones transmit info. as electrical impulses, these impulses pass along the axon of the nerve cells- made from the nerve cell's cytoplasm stretched out into a long fibre and surrounded by a cell membrane. Some axons are also surrounded by a fatty sheath that acts as an insulator, shielding the neurone from neighbouring cells and speeds it up 
  • Electrical impulses trasmit info. v quickly so respsonses happen fast, but they are short-lived. Hormones are also used to carry info. around the body, they're produced in the glands and travel around in the blood, responses come about slower and they're longer lasting.
  • A synapse is a tiny gap between neurones, informations is transferred from one to another across a synapse, this is dont using transmitter chemicals: when an electrical impulse reaches the end of a neurone it triggers the release of transmitter chemicals into the synapse. These transmitter chemicals diffuse across the gap and bind to receptor molecules on the membrane of the next neurone. Only specific transmitter chemicals can bind to the receptor molecules on the neurone. When the chemicals bind to the right receptors they trigger a new electrical impulse in the next neurone. 
  • Drugs can affect transmission across synapses e.g. one way ecstasy works is by blocking sites in the brain's synpases where serotonin is removed, bc it can't be removed conc. increases, affecting a person's mood. 
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  • Reflexes are involuntary responses, they are rapid automatic responses to a certain stimuli. The route taken by the info in a reflex (receptor by effector) is called a REFLEX ARC- which goes through the spinal cord or an unconscious part of the brain. 
  • When a stimulus is detected by receptors an impulse is sent along the sensory neurone to CNS. In the CNS the message is passed on to the relay neurone which passes the impulse to a motor neurone.  The impulse then travels along the motor neurone to the effector. 
  • The effector then responds. An impulse always takes the same, direct route through the reflex arc so no info. is ever processed. This is why reflexes are involuntary and rapid.
  • Simple reflexes improve chance of survival- simple animals  have no brain and rely entirely on simple reflex actions which cause them to respond to some stimuli in a way that helps them survive. E.g. finding food and sheltering from predators.
  • Humans also have simple reflexes that may protect them from damage or increases chances of survival e.g. v bright light can damage the eye so muscles in the eye contract making the pupil smaller. Reflex to drop hot things. Newborns have reflexes that are lost: automatically suckling from their mothers, graspiing when palms are touched, taking steps when on a flat surface. 
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Modifying and learning responses

  • In some cases it's possible to modify a natural reflex response e.g. when you pick up a hot object you'll want to drop it (the reflex response to avoid skin damage), dropping the plate might not be the best idea, so responses can be overriden by a neurone betweem the brain and the motor neurone of the reflex arc. 
  • Reflex responses can also be learned- a stimulus causes a particular reflex response, but animals can learn to produce the same response to a new (secondary) stimulus- this is conditioning. The new reflex is called a conditioned reflex.
  • Pavlov's dogs are a good example: he studied behavoir og dogs and noticed they'd salivate when they smelt food- a simple reflex to a primary stimulus. He experimented by ringing a be;; just before dogs were given food, after a while he found the dogs salivated when the bell was rang, even if they couldn't smell food. Dogs responded to a secondary stimulus, this is a conditioned reflex and the final response has no direct connection to the secondaty stimulus.
  • Conditioned reflexes can increase chance of survival e.g. some animals are brightly coloured to stand out, this is become insects with bright colouring are often poisonous, their colour acts as a warning to predators. The predators developed a conditioned reflex to a secondary stimulus (colour) to stay away, increasing insects chance of survival. 
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Brain Development and Learning

  • Brain is essentially lots of neurones all interconnected, it contains billions of things- this means it can modify behaviour as a result of experience and coordinate behavior- social. 
  • Environment can affect brain development and learning- the brain of a newborn is only partly developed, most of the neurone connections are not yet formed- it becomes more and more developed with every new experience. Connections form as the child experiences new things- when a neurone is stimulated by the experience it branches out, connecting cells that were previously unconnected. By the age of three most of the connections that will ever form have been formed, making a huge network of neurones with trillions of possible routesfor nerve impulsesto travel down. No. remains fairly constant until approx. 10yrs old. 
  • You learn throughout you life, when experiences are repeated over and over again, pathways the nerve impulses travel down becomes strenghtened, these strenghtened pathways are more likely to transmit impulses than others, which is why practise makes things easier. After the age of ten, pathways that are not used as often will die off, which is why it is harder for adults to learn new things. 
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Learning Skills and Behaviour

  • Being able to learn means you can adapt to new situations, complex animals are v adaptable, they are able to cope with a lot. They are adaptable because of the variety of potential pathways in the brain. Simpler animals have less flexible nervous systems so their behaviour is much more predictable and less adaptable. 
  • Some scientists believe there are definite stages of a child's brain, nerve pathways need to be strenghthened at a certain age, otherwise it is too late. E.g. the ability to communicate by language depends on a child hearing other people speak, it is thought that they must hear during a certain critical period, if children haven't learnt by the age of 10, they probably never will. Evidence for this comes from feral children. 
  • Cerebral Corbex is an important part of the brain- the brain is a very complex organ and the CC is the outer part of the brain. It has a folded structure, making the brain look wrinkled. 
  • The CC plays a large roles in things like: intelligence, memory, language, consciousness. 
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Studying the Brain

  • Scientists use a range of methods to study the brain: Studing patients with brain damage- observing any effects of the damage gives an indication of what it does. Electrically stimulating the brain- push a tiny electrode into the tissue and giving it a small amount of electricity. By observing the effects of stimulating parts of the brain does, it gives an idea of what that part does. MRI Scans- scientists use to produce very detailed pictures of the brain's structure, use it to find out what parts of the brain are active. 
  • Memory is the storage and retrieval of information. Firstly, you have to store information and then retrieve it- there are two main types of memory: Short-term= lasts for anything from a few seconds for a few hours, used for info you're thinking about at that moment. Long-term memory= memories that were stored for days, months, even years ago. 
  • Humans are more likely to remember things when they can see a pattern in the information, or if it is associated with a strong stimuli. Repetition also helps.
  • No one knows for sure how memory works, there are lots of different models to try and explain it, some scientists think the multi-store model offers a good explanation- info you've paid atttention to is temporarily stored in short-term memory, if it is repeated enough it is transferred to long-term and stored there, things that aren't transferred to long-term can be forgotten. So far, no model has provided satisfactory explantion of human memory. 
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