Biology Additional Science

Animals and plant cells have

• Nucleus: controls cells activities
• Cytoplasm: where many chemical reactions take place
• Cell membrane: controls the movement of materials
• Mitrochondria: where energy is released during aerobic respiration
• Ribosomes: where proteins are made (synthesised)

Plant cells also have

• Cell wall: for support
• Chloroplasts: contain chlorophyll for photosynthesis

• As organisms develop some of the celss chnage and become specialised to carry out particular jobs
• This is called differentation
• Differentation happens much earlier in the development of plants than it does in animals
• In plants they may become xylem or root hair cells
• In animals they may become nerve or sperm cells

• Diffusion is the random movement of molecules from an area of high concentration to low concentration
• The larger the difference in concentration the faster the rate of diffusion
• Examples of diffusion are oxygen in to the cells of the body from the blood strean as the cells are respiring
• Also carbon dioxide in to actively photosynthesising plant celss
• Also simple sugars and amino acids from the gut through the cell membranes
• Diffusion does not require any energy from the cell

• Is the movement of water
• A special case of diffusion involving a partially permeable membrane
• Just like diffusion the movement of molecules is ransom and requires no energy from the cell
• Osmosis is the diffusion of water across a partially permeable membrane from a dilute solution to a more concentrated solution
• No solute molecules can more across the membrane
• Water is needed to support the celss and because chemical reactions take place in the solution

• The word equation is: carbon dioxide+water+light energy=glucose+oxygen
• Photosynthesis can only be carried out in green plants
• Chlorophyll traps the suns energy

The structure of a leaf

• The upper epidermis contains a waxy layer which is waterproof so it stops water loss
• The palisade layer contains the palisade cells that are at the top of the leaf, close to the light, tightly packed together and full of chloroplasts
• The spongy layer contains cells that are not packed tightly together so they have a large surface area available for gas exchange, also some chloroplasts and air spaces
• The lower epidermis contains guard cells that open and close the stomata to control water loss. Also the stomata that allows gases to move in and out of the leaf

• The carbon dioxide concentration may be limited in an enclosed space, for example a greenhouse on a sunny day
• Light intensity may be limited on the floor of a rainforest
• The tempreture is a limiting factor becasue otherwise the enzymes will not work effectively

• The product of photosynthesis is glucose
• Glucose is used in respiration
• Glucose is combined with other nutrients by the plant to produce new minerals
• Glucose is stored by the plant as an insoluble starch so it is not effected by osmosis

• Plants produce sugars through photosynthesis
• Nitrates are taken from the soil to produce amino acids
• These are used to make proteins for growth
• A plant that is nitrate deficient will have stunted growth
• Magnesium is essential to produce chlorophyll
• A plant that is magnesium deficient will have yellow leave

• A pyramid of biomass represents the mass of all the organisms at each stage in the food chain
• A pyramid of biomass is likely to give a more accurate picture than a pyramid of numbers
• Becuase for example one bush may have many insects feeding on it but the mass of the bush is far greater than the mass of the insects

• Not all food eaten can be digested, some energy is lost ub faeces, respiration, movement and keeping a constant tempreture
• Not all the energy taken in by an organism results in the growth of that organism

• The shorter the food chain the less energy will be lost
• It is more efficient for us to eat plants that animals
• We can produce meat more efficiently by preventing the animals movement and keeping the animals at a constant tempreture

• Detritus feeders such as worms may start a process of decay by eating dead animals or plants and producing waste products
• Then decay organisms break down the waste and dead plants and animals
• Decay organisms are micro-organims
• Decay works faster when it is warm and wet
• All the materials from waste and dead animals are recycled

• Photosynthesis removes carbon dioxide from the atmosphere
• Green plants and animals respire which returens carbon dioxide back in to the atmosphere
• Animals eat green plants and they build the carbon up in their bodies
• When animals and plants die the release carbon dioxide back in to the atmosphere
• A stable community recycles all of the nutrients it takes up

• Enzymes are biological catalysts, they speed upo reactions
• Enzymes are large proteins and each has a particular shape
• The shape where the other molecules fit in is called the active site
• When the tempreture is abov fourty degrees the enzymes will loose its shape and become denatured
• Enymes lower the amount of energy needed for a reaction to take place, the activation energy

• Reactions take place faster when it is warmer
• At a higher tempreture the molecules move around quicker and they collide with each other more often and with more energy
• Tempreture affects the enzyme
• If the Ph is too acidic or alkaline then the active site could change shape

• Glucose+oxygen=carbon dioxide+water+energy
• The process takes place in the mitrochondria
• Aerobic respriration is the realase of energy from food when oxygen is availble
• The energy released is used to build larger moleclules from smaller ones. Also enable muscle contractions in animals. Also maintain a constant body tempreture in mammals and birds and to build sugars, nitrates nutrients in plants. Which then turn in to amico acids which are proteins

• Digestion involes the breakdown of large insoluble molecules in to smalller soluble ones
• Amayase is a carbohydrase that is produced by the salivary gland, pancreas and the small intestine
• It catalyses the digestion of starch in to sugars in the mouth and small intestine
• Protease is produced by the stomach, pancreas and small intestine
• It catalyses the breackdown of proteins in to amino acids in the stomach and small intestine
• Lipase is produced by the pancreas and the small intestine
• It catalyses the break down of lipids which are fats and oils in to fatty acids and glycerol

• Amylase and lipase work in the small intestine
• They work best when the conditions are slightly alkaline
• Protease works in the stomach and when the condition are acidic
• Glands in the stomach wall produce hydrocloric acid to create very acidic conditions
• The liver produces bile that is stored in the gall bladder
• Bile is squirted in to the small intestine and neutralises the stomach acid
• It makes the conditions slightly alkaline

• Biological washing powder contains enzymes that digest food stains
• They work at a lower tempreture which saves money and energy
• Protease pre-digests proteins in baby foods
• Isomerases converts glucose in to fructose
• Fructose is much sweeter so less is need which makes it less fattening so it is used in diet foods
• Carbohyrase converts starch in to sugar syrup for use in foods

• This is called homeostasis
• Carbon dioxide is a waste product so it is excreted by the lungs
• Some of the amino acids we take in are not used
• These get converted in to urea by the liver and is excreted by the kidneys in the urine
• Urine can be stored in the baldder
• The water and ion content must be controlled
• If they are not then to much or to little may move in and out of the cells by osmosis

• The thermoregulatory centre in the brain and the receptors in the sking detect changes in tempreture
• The thermoregulatory centre controls the responses to internal tempreture

If the core tempreture rises:

• Blood vessles near the surface dialte causing more blood to flow through the capillaries, vasodilation
• Therfore heat is lost by radiation
• Sweat glands produce more sweat which evaporates of the skin
• The energy required for it to evaporate cones from the skins surface so we cool down

If the core tempreture falls:

• Clood vessels near the surface constrict causing less blood to flow through the capillaries, vasocontstriction
• Therefore less heat is radiated
• We shives which make the muscles contract
• This requires respiration and some of the energy produced is released as heat

• The pancreas monitors and controls the level of sugar in our blood
• If there is too much sugar in our bllod the pancreas produces insulin
• That results in the excess sugar being stored in the liver as glycogen
• If insulin is not produced the blood sugar levek may become fatally high
• If the pancreas is not producing enough insulin it is called type one diabetes
• It can be controlled by diet or inslulin injections

• Body cells need to divide to produce news cells for growth and repair
• Mitosis results in two identical cells being produced from the original cell
• A copy of each chromosome is made before the cells divides and one of each chromosome goes to each cell making them identical

• Stem cells are unspecialsed
• They can develop, differntiate in to many types of speacialised cells
• Stem cels are found in the the embryo and in adult bone marrow
• Many embryonic stem cellls are from aborted embryos or a spare embroyo from fertility treatments
• This raises ethical issues
• The use of stem cells from adult bone marrow is limited by the number of differnent types of specialised cells we can develop them in to

• Cells in reproduction organs diveide in to sex cells called gametes
• Before devision a cope of each chromosome is made
• The cell now divides twice to form four gametes
• This is called meiosis
• Sexual reproduction results in variation as the sex cells from each parent fuse
• So half the genetic information if from your father and the other half from your mother

• Gregor Mendel was a monk who worked out how charteristics are inhrerited
• Genes are short lengths of DNA (deoxyribonucleic acis)
• These make up chromosomes and control our characteristics
• Genes are a code of combinations of specific amino acids
• Which make up proteins

• Humans have twenty-three pairs of chromosomes
• Femals are **
• Males are XY
• Genes controlling the same characteristics are alleles
• If am allele is masks the effect of another it is dominent
• The allele wherer the effect is masked is a recessive
• For example the allele for brown eyes is dominent over the allele for blue eyes

• Huntingtons disease is a disorder of the nervous system
• It is caused by a dominent allele
• So evern if one parent has the disease it can be inherited by the child
• Cystic fibrosis is a disorder of cell membranes
• It is caused by a recessive allele
• Only if both parents are either carriers of have the disorder can the child inherit it
• Embroys can be screemed to see if the carry an alleles for one of these genetic disorders