AQA biology unit 2

Animal and plants cells;nucleus, cytoplasm, cell membrane, mitochondria.

plants cells also have; cell wall, chloroplasts, vacuole.

• substances pass into and out of a cell by diffusion.
• water passes into and out of a cell by osmosis.

diffusion- movement of particles from a high concentrated area to a low.

osmosis- movement of water across a partially permeable membrane from high water concentrated area to a low.

• nucleus- controls activities in the cell
• cytoplasm- chemical processes happen
• cell membrane- controls the movement of substances in and out of the cell
• mitochondria- energy by respiration is released.
• cell wall- supports and strengthens the cell
• chloroplasts- contain chlorophyll, used for photosynthesis.
• vacuole- filled with sap to help keep the cell turgid.

photosynthesis- the chlorophyll in the leaves absorb light. the light is used to react carbon dioxide with water to make glucose. the glucose can be used in respiration or converted into starch and stored. oxygen is also produced.

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

for photosynthesis to occur the plant needs four main things;

• light- from the sun
• chlorophyll- absorbs the light
• carbon dioxide- enters from surrounding air
• water- from the soil

light, co2 concentration and temperature need to be monitored for photosynthesis to occur in the best way.

the glucose produced from photosynthesis is important for their survival,

• respiration- to help build new cells and grow
• making fruit- glucose and fructose is turned into sucrose for storing in fruits
• making cell walls- glucose is turned into cellulose
• making proteins- glucose is combined with nitrates to make amino acid which can be used to make proteins.
• stored in seeds- glucose is turned into lipids for storing in seeds.
• stored as starch- glucose is turned into starch and stored in the roots, stems and leaves ready for use when photosynthesis cannot be done, eg; in the winter.

plants need carbon, hydrogen and oxygen to survive.

plants also need minerals to survive. if minerals are deficient then the plant may suffer from poor growth. they are absorbed through the roots ad mineral ions dissolved in the coil water. two important minerals are

• nitrate- for making amino acids which are needed to make the proteins. deficiency can cause a stunted growth
• magnesium- for making chloraphyll. defficiancy can cause yellow leaves.

the efficiency of food can be improved by reducing the amount of energy lost to the surroundings. eg; stopping animals moving around to much and keeping the surroundings warm.

pigs and chickens are often kept in warm sheds, this allows little room to move around which allows more efficient food production. this causes concern about the lives of animals.

how to calculate efficiency-

total energy eaten-energy wasted (faeces etc)=energy released by respiration.

this final product is the origianal energy available to the next stage.

all cells contain carbon because they all contain protein, fat, and carbohydrates. carbon is passed from the atmosphere as co2 to living things and returned to the atmosphere. this is known as the carbon cycle.

materials rom living things decay because microorganisms digest them. this process happens faster in warm conditions with plenty of oxygen.

during the decaying process, co2 is releases back into the atmosphere as the organisms respire.

enzymes are proteins that denature at around 45'C. they are very important in respiration and digestion.

digestion- the breaking down of carbohydrates, proteins and fats into small soluble substances that can be absorbed into the blood.

enzymes are are also proteins that are folded into complex shapes to allow smaller molecules to fit into them. the place where the substrate molecule fits in is called the active site.

if the shape of the enzyme changes then its active site may no longer work. this means the enzyme has been denatured. this can be done by extremes of ph or high temperatures.

as the temperature increases, the rate of reaction increases untill the temperature reaches too high and the enzyme denatures.

changes in ph alter the shape of the enzyme. for most enzymes, the optimum ph is 7.

some enzymes work outside of the cells, the main group of these are the digestive enzymes. they are either produced by the glands, or by specialised cells lining the digestive tract. the purpose of these enzymes is to speed up the breakdown of large molecules which can be abosrbed into the blood.

enzymes have their own uses,

• protease- to pre-digest proteins during the making of baby food
• lipase- biological detergants to break down substances in stains into small water soluble substances
• carbohydrase- to convret starch syrup into sugar syrup which is more valuable.

the digestive system is quite complicated and each place has a different job,

• salivary glands- produce amylase enzyme in the saliva
• liver- bile is produced. it neutralises stomach acid and emulsifies fats
• gall blader- bile is stored before it is released into the small intestine
• large intestine- excess water is absorbed from the food
• rectum- the faeces are stored before they leave through the anus
• small intestine- produces protease, amylase and lipase enzymes to complete digestion. food is absorbed out of the digestive system into the body
• pancreas- produces protease, amylase and lipase enzymes. it releases these into the small intestine.
• stomach- pummels the food with its muscular walls. produces thr protease enzyme, pepsin. produces hydrochloric acid to kill bacteria and to give the right ph for the protease enzyme to work.

homeostasis is the word used to describe howliving things maintain a constant internal envioronment.

in humans there are three key areas that are controlled,

• core body temperature
• water balance
• blood sugar level.

the thermoregulatory centre in the brain contains receptors that are sensitive to the temperature of the blood flowing to the brain. it also receives impulses from the skin, providing information about the skins temperature. your body can then respond to try to cool or warm you.

to heat you up,

• hairs stand up which traps air to insulate
• no sweat is produced
• blood vessels supplying the skin capillaries constrict to close-off the skin's blood supply
• you shiver which needs respiration which releases some energy as heat.
• vasoconstriction occurs.

urea is produced in the liver whn excess amino acids are broken down.

energy is transferred along food chains from wone stage to the next, but not all of the energy available can be absorbed by the next organism. it decreases from one stage to the next.

some of the energy goes into growth and the production of offspring. this becomes available to the next stage but most is used up in other ways,

• respiration- used for movement and other life processes and is eventually lost as heat to the surroundings
• waste- such as faeces.

the energy used in these ways is returned to the envioronment.

their are rarely more than four stages to a food chain because the energy lost is so great at each stage.

respiration is different to breathing. it is a chemical process where energy is released from food substances such as glucose.

aerobic respiration needs oxygen. most of the chemical reactions involved in the process happen in objects inside the cell cytoplasm called mitochondria.

glucose + oxygen = carbon dioxide + water (+energy)

The energy released in respiration is used to make large molecules from smaller ones. the energy is also used to allow muscles to contract in animals and maintain a constant body temperature in birds and mammals.

photosynthesis- the chlorophyll in the leaves absorb light. the light is used to react carbon dioxide with water to make glucose. the glucose can be used in respiration or converted into starch and stored. oxygen is also produced.

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

for photosynthesis to occur the plant needs four main things;

• light- from the sun
• chlorophyll- absorbs the light
• carbon dioxide- enters from surrounding air
• water- from the soil

light, co2 concentration and temperature need to be monitored for photosynthesis to occur in the best way.

the glucose produced from photosynthesis is important for their survival,

• respiration- to help build new cells and grow
• making fruit- glucose and fructose is turned into sucrose for storing in fruits
• making cell walls- glucose is turned into cellulose
• making proteins- glucose is combined with nitrates to make amino acid which can be used to make proteins.
• stored in seeds- glucose is turned into lipids for storing in seeds.
• stored as starch- glucose is turned into starch and stored in the roots, stems and leaves ready for use when photosynthesis cannot be done, eg; in the winter.

plants need carbon, hydrogen and oxygen to survive.

plants also need minerals to survive. if minerals are deficient then the plant may suffer from poor growth. they are absorbed through the roots ad mineral ions dissolved in the coil water. two important minerals are

• nitrate- for making amino acids which are needed to make the proteins. deficiency can cause a stunted growth
• magnesium- for making chloraphyll. defficiancy can cause yellow leaves.