Biology B2A

additional science:-

  • cells
  • plants
  • food chains and cycles
  • enzymes
  • homeostasis
  • cell division
  • inheritance
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cells keywords:

animal cells.

plant cells.

nucleus-contains genetic info which controls activities of the cell.

cytoplasm-controlled by enzymes. most chemical processes take place here.

cell membrane-controls the movement of substances in and out of the cell.

vacuole- cell sap to keep cell turgid.

cell wall-strengthens the cell.

chloroplast-contain chlorophyll which absorbs energy for photosynthesis.

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mitochondria-most energy is released by respiration here.

ribosomes-protein synthesis happens here.

red blood cells-no nucleus. contain haemoglobin to carry oxygen to the cells. oxygen can diffuse through easily. 

root hair cells-large surface area. finger-like structure with a very thin cell wall. absorbs water and mineral ions from the soil.

sperm cells-head contains genetic info and a enzyme to penetrate the egg cell. middle section packed with mitochondria for energy. long tail. fertilises egg cell.

leaf cells-absorbs light for photosynthesis. packed with chloroplasts. close packed cells form a layer for efficient absorption of sunlight.

differentiation-cells are specialised for a particular function. their structure helps their function.

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osmosis- water can move across cell membranes. movement is random and requires no energy from the cell. 

  • 2 solutions with different concentrations.
  • a partially permeable membrane to separate them.

movement of water from a less concentrated solution to a more concentrated solution through a partially permeable membrane. no solute molecules can move across it. 

water is needed to support the cells; chemical reactions take place there. plants gain water through osmosis. 

diffusion- movement of particles from an area of higher concentration to an area of lower concentration. 

larger the concentration difference, faster the rate of diffusion. 

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Plant keywords:

photosynthesis- carbon dioxide + water (+light energy) = glucose + oxygen

carbon dioxide is taken in by the leaves, and the water by the roots. chlorophyll traps the energy needed for photosynthesis. oxygen is given off as a waste gas and the sugar glucose is made. 

limiting factors- limit the speed of photosynthesis.

  • light intensity
  • carbon dioxide concentration
  • temperature

farmers use limiting factors to increase growth in greenhouses- 

  • artificial lights- photosynthesis continues during nighttime.
  • paraffin lamps- produces carbon dioxide and heat.
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minerals- elements to stay alive.

  • carbon
  • hydrogen
  • oxygen

plants need minerals for healthy growth.

  • nitrate ions- making amino acids, which make proteins.
  • magnesium ions- making chlorophyll.

if a plant does not get enough minerals it's growth will suffer from deficiency symptoms. nitrate- stunted growth. magnesium- leaves go yellow.

glucose- product of photosynthesis. used for respiration.

glucose is combined with other nutrients by the plant to produce new minerals. glucose is stored in some plants, as insoluble starch. it is stored as an insoluble substance so that it has no effect on osmosis.

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Food chains and cycles

food chain and cycles keywords: 

energy in food production- shorter the food chain, the less energy will be lost. more efficient to eat plants than animals. efficiency of food production can be improved by reducing the amount of energy lost to its surroundings. 

  • stop animals moving around too much- waste energy on movement.
  • warmer temperatures- waste energy on trying to keep itself warm, from food.
  • balance must be made between consumers and farmers.

decay- detritus feeders start the process of decay by eating dead animals of plants and producing waste materials. dead organisms then break down the waste and dead plants and animals. decay organisms are microorganisms. decay is faster if it is wet and warm. recycled.

stable community recycles all of the nutrients it takes up- carbon cycle. 

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Food chains and cycles

biomass- pyramids of biomass show the mass of living material at each stage in a chain. the amount of material and energy decreases from one stage to the next. 

food production is more efficient if the chain is short or if energy losses from animals are reduced. 

carbon cycle- shows how carbon moves from the atmosphere , through various animals and plants, and then back to the atmosphere. 

more accurate than pyramid of numbers. 

energy losses- energy is lost in faeces because not all food eaten is digested.

  • respiration- movement and growth
  • production of offspring.

all of the energy used above return to the environment and is not available to the next stage.

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Enzyme key words:

enzymes- biological catalysts (speed up reactions). large proteins and each have a particular shape. the shape has an area where other molecules can fit. this is called the active site

too high temperature- change enzymes shape and denature the enzyme. 

too high pH- change enzymes shape and denature the enzyme. different enzymes work best at different pH values. if the pH is too alkaline or acidic the enzyme will denature.

enzymes can catalyse the build up of small molecules into large molecules or, the breakdown of large molecules into small molecules.

as temperature increases, rate of reaction increases. enzymes lower the amount of energy necessary for a reaction to take place- activation energy.

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enzymes in digestion- breakdown of carbs, proteins and fats into small soluble substances that can be absorbed into the blood. 

  • amylase- produced by salivary glands, the pancreas and the small intestine. catalyses the starch into sugars in the mouth and small intestine.
  • protease- produced by the stomach, the pancreas and the small intestine. catalyses the breakdown of proteins into amino acids in the stomach and small intestine.
  • lipase- produced by the pancreas and small intestine. catalyses the breakdown of lipids (fats and oils) to fatty acids and glycerol. 

speeding up digestionprotease enzymes work best in acid conditions (stomach). glands produce hydrochloric acid to create very acidic conditions.

amylase and lipase- slightly alkaline (small intestine).

liver produces bile. stored in gall bladder. goes into small intestine and neutralises the stomach acid. makes it slightly alkaline. 

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use of enzymes-biological washing powders contain enzymes that digest food stains. work at low temperatures so they save money.

protease- pre digest proteins in some baby foods.

isomerase- convert glucose into fructose. fructose is sweeter so less is needed in foods.

carbohydrases- convert starch into sugar syrup for use in foods.

aerobic respiration- glucose + oxygen = carbon dioxide + water + energy.

enzymes in cells catalyse photosynthesis, protein synthesis and aerobic respiration. takes place in mitochondria.

energy released is used to:

  • build larger molecules from smaller ones.
  • enable muscle contraction and maintain constant body temperature.
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homeostasis key words:

controlling body temp- too hot:

  • sweat glands release more sweat. it evaporates, removing heat and energy from the skin.
  • blood vessels leading to skin capillaries become wider (dilate) allowing more blood to flow through the skin, and more heat to be lost.

too cold:

  • muscles contract rapidly- we shiver. these contractions need energy from respiration and some is released as heat. 
  • blood vessels become narrower (they constrict) letting less blood flow through the skin and conserving heat in the body.
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controlling blood sugar- pancreas monitors and controls the level of sugar in our blood. too much sugar in the pancreas produces the hormone insulin that results in the excess sugar being stored in the liver as glycogen

if insulin is not produced the blood sugar level may become fatally high. 

known as diabetes. controlled by diet or the person taking insulin injections. 

controlling body temperature- thermoregulatory centre of the brain and receptors in the skin detect changes in temperature. thermoregulatory centre controls the body's response to a change in internal temperature. 

work best at 37 degrees- temp is controlled. 

thermoregulatory centre gathers information as nerve impulses from temperature receptors in: 

  • the brain- sensitive to the tempature of the blood flowing there.
  • the skin- sensitive to skin temperature.
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controlling internal conditions-processes in your body that help to maintain a constant internal environment are known as homeostasis. 

  • water content
  • ion content
  • body temperature
  • blood glucose concentration

waste products must be removed from the body. if not, they will increase in concentration and may interfere with chemical reactions or damage cells.

carbon dioxide- product of aerobic respiration. removed through lungs when we breathe out.

urea- produced in the liver when excess amino acids are broken down. kidneys remove it from the blood and make urine, which is stored in the bladder temporarily.

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Cell division

cell division key words:

necessary for the growth of an organism or for repair if tissues are damaged. 

mitosis results in two identical cells being produced from the original cell. copy of each chromosome is made before the cell divides and one of each chromosome goes to each new cell.

stem cells- unspecialised. differentiate into many different types of specialised cells. stem cells are found in the embryo and in adult bone marrow. 

cell division in sexual reproduction- cells in reproductive organs (testes and ovaries) divide to form gametes (sex cells). 

before division, a copy of each chromosome is made. the cell now divides twice to form four gametes. this type of cell division is called meiosis each gamete has only one chromosome from the original pair. all of the cells are different from each other and the parent cell. 

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inheritance keywords:

mendel- worked out how characteristics were inherited. ideas not accepted for many years. genes are short lengths of DNA which make up chromosomes and control our characteristics. genes code for combinations of specific amino acids, which make up proteins. 

inheritance in action- humans have 23 pairs of chromosomes (one pair are sex chromosomes). females are ** and males are XY. genes controlling the same characteristics are called alleles. 

if an allele masks the effect of another it is said to be dominant. the allele where the effect is masked, it is said to be recessive

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inherited conditions in humans- Huntington's disease is a disordr of the nervous system. caused by a dominant allele, so even if only one parent has the disease it can be inherited by a child. 

cystic fibrosis is a disorder of cell membranes. caused by a recessive allele so parents could be carriers (Cc). only if both parents are either carriers or have the disorder does a child inherit it. 

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