paper two

what is a cell

smallest unit of life that can replicate independently

what type of cell is an animal

eukaryotic

what type of cell is bacteria

prokaryotic

what is the purpose of a cell membrane

control which substances pass in and out of the cell

what is the purpose of a nucleus

contains DNA

what is the purpose of cytoplasm

site of chemical reactions

what is the purpose of mitochondria

provide cells with energy

what is the purpose of ribosomes

site of protein synthesis

what organelles do animal cells contain

• cell membrane

• ribosomes

• mitochondrion

• nucleus

• vacuole

• cytoplasm

what organelles to plant cells contain

• cell wall

• vacuole

• chloroplasts

• nucleus

• mitochondria

• cytoplasm

• cell membrane

• ribosomes

what is the purpose of a cell wall

support and structure

what is the purpose of the vacuole

contains cell sap

what is the purpose of the chloroplasts

where photosynthesis happens

→ contains chlorophyll which absorbs light energy

what organelles does a bacteria cell contain

• ribosomes

• cell wall

• cell membrane

• cytoplasm

• chromosomal DNA

• plasmids

• flagellum

what is the purpose of plasmids

store extra DNA

what is the purpose of flagella

tails to propel the bacteria forwards

what is diffusion

the net movement of particles form an area of higher concentration to an area of lower concentration in gases and liquids

• sometimes through a partially permeable membrane

what factors can affect rate of diffusion

• concentration gradient

• temperature

• surface area

what is osmosis

the net movement of water molecules across a partially permeable membrane from a region of high water concentration to a region of lower water concentration

what is active transport

the net movement of molecules from a lower concentration gradient to a higher concentration requiring energy from cellular respiration

• always across a cell membrane

root hair cell adaptations

• lots of mitochondria for active transport

• large surface area for osmosis

what is an enzyme

a biological catalyst

what is a catalyst

a substance which increases the speed of a reaction without being changed in the process

how do enzymes work

they have an active site which is complementary to the shape of the substrate. the enzyme can change shape slightly to fit the substrate

what happens to enzymes as temps increase

originally enzyme activity increases but once we reach 37 degrees the bonds in the enzyme begin to break so it starts to denature. rate of reaction will start to slow down but eventually it will not be able to bind at all

what is the optimum temp meaning

the temperature where the rate of reaction is highest

what is the optimum pH of an enzyme

7 (except digestive enzymes in stomach acid)

carb breakdown

starch → (amylase) → maltose → (maltase) → glucose

protein breakdown

protein → (protease) → amino acids

lipids breakdown

lipids → (lipase) → glycerol and fatty acids

where is amylase made

• pancreas

• small intestine

• salivary gland

where is protease made

• pancreas

• small intestine

• stomach

where is lipase made

• pancreas

• small intestine

where is maltase made

• pancreas

• small intestine

how big is a cell

between 1 and 100 micrometres

image meaning

the image we see in a microscope

magnification calculation

magnification = image/object size

resolution meaning

the shortest distance between two points on an object that can still be distinguished as two separate entities

pros of a light microscope

• easy to use

• cheap

pros of an electron microscope

• higher resolution

• higher magnification

species meaning

the same organisms

populations meaning

a group of the same species in the same area at the same time

habitat meaning

where the organism lives

community meaning

all the populations living in the same area at the same time

benefits of diversity

1. increases stability of ecosystem

2. many species provide a specific service

3. many medicinal drugs

eutrophication explanation

fertiliser (containing nitrates and phosphorus) from fields runs into ponds/rivers (via leaching) → promotes excessive algal growth → blocks sunlight = less photosynthesis → less oxygen → plant and animal death → less oxygen (also decomposers use up oxygen). this affects the water and therefore crops and people/animals

explain a parasitic relationship

the parasite lives in or on the body of the host and steals resources. the host is often harmed in some way

explain a mutualistic relationship

both organisms benefit in some way, for example flowers and bees

name abiotic factors in a ecosystem

• light intensity

• temperature

• water levels

• soil pH

• soil minerals

• wind

• carbon dioxide

• oxygen

name biotic factors in the ecosystem

• new predators

• animals

• plants

how much biomass is transferred to the next trophic level

around 10%

why is only 10% biomass

1. the animal may not eat all of the biomass of the previous trophic level

2. the animal may not absorb all the biomass (excretion)

3. lots of biomass is used for non-useful stores (life processes)

efficiency of energy transfer calculation

efficiency = biomass in higher trophic level/lower x 100

how to use a quadrat to measure abundance

1. place tape measures along the length + width of the field (forming a large grid)

2. randomly generate x pairs of random coordinates

3. place quadrats at those coordinates and count how many X are found in each quadrat.

4. calculate the mean number of X per m^2.

5. estimate the total population size using our mean number of X per m^2 times the total area of the field

how to use a transect to find distribution

1. a transect line (tape measure) is laid out in a straight line between the X and X places

2. X quadrats are placed at regular intervals along the transect line

3. the distribution of X is measured by counting the number of X in each quadrat along the transect line, (from the lake to the woodland)

   repeat this using new transect lines (parallel to the first).

what to blood worms indicate

indicate levels of water pollution because they thrive in adverse, low oxygen conditions

what do sludgeworms indicate

high levels of water pollution because they thrive in adverse, low oxygen conditions

what do freshwater shrimp indicate

very clean water because they need very clean water to survive

what do stone fly larvae indicate

clean water. they will only be laid on very clean water or else they won’t survive

what do black spot fungus indicate

they are very sensitive to sulphur dioxide, if there are high levels in the air or rain they will not be able to grow

what do bushy lichens indicate

need very clean air to survive

what to leafy lichens indicate

can survive in moderately clean air

what do cru5ty lichens indicate

they can survive in more polluted air

food security definition

when all people at all times have physical and economical access to safe, sufficient and nutritious food and is sustainable for the planet into the future

what things decrease food security

• conflicts

• increasing human population

• increasing fish and meat consumption

• new pests and pathogens

• climate change

what is decay

the breakdown of organic matter by decomposers

what are the best temperatures for decomposition

10 to 40 degrees

why do we keep food in a fridge/freezer

the organisms will be less active so there will be less decomposition

why do we vacuum pack or package things in nitrogen gas

because decomposers need oxygen to survive because they are aerobic

what is composting and why is it good

decaying biomaterial which can be used as a fortifier for other crops due to the minerals it contains

why do we dry things or put it in salt

decomposers cannot survive with no water and also decomposition is a chemical reaction and it can’t occur without oxygen

what are decomposers

microorganisms such as bacteria or fungi

what are detritus feeders

small animals which feed on dead organic matter

mean rate of decomp calculation

mean rate of decom = mass lost/number of days

units of mean rate of decomp

g/day

why does nitrogen need to be in nitrate form

plants uptake it from the soil and animals eat it but only when it is in nitrate form

nitrogen cycle → lightning

converts atmospheric nitrogen into ammonia and nitrates by combining nitrogen gas with water and then falling in precipitation to the ground

parts of the nitrogen cycle

• nitrogen fixation

• nitrification

• denitrification

• decomposition

• assimilation

nitrogen cycle → nitrifying bacteria

nitrogen gas is converted to ammonia in the soil by nitrifying bacteria

where can nitrifying bacteria be found

in plant roots of leguminous plants or free-living in soil

nitrogen cycle → nitrification

aerobic, nitrifying bacteria convert ammonia in the soil to nitrates

process of nitrification

ammonia → (nitrosomonas) → nitrites → (nitrobacter) → nitrates

nitrogen cycle → denitrification

denitrifying bacteria use nitrates as a food source and release nitrogen gas

nitrogen cycle → decomposition

decomposers produce ammonia from the breakdown of amino acids and proteins

nitrogen cycle → assimilation

plants use nitrogen to build biological molecules which is then incorporated into the plants ‘body’

what is crop rotation and why

in agriculture the nitrogen content of the soil will decrease overtime since crops are harvested instead of decomposed. rotating crops and including a nitrogen fixing plant replenishes nitrogen in the soil

process of carbon cycle

1. carbon is found everywhere

2. carbon is used for photosynthesis in plants

3. it makes glucose

4. heterotrophs feed on this

5. heterotrophs respire

6. heterotroph dies and is eaten by decomposers which respire

7. carbon in fossil fuels which we burn

water cycle explanation

1. evaporation

2. transpiration

3. condensation

4. precipitation

5. infiltration

how does desalination work

salt water is forced through a partially permeable membrane by high pressure, the salt and other impurities can’t get through

why do humans need specialised exchange surfaces

as organisms get larger their surface area to volume ratio decreases because volume increases three times faster than surface area so for diffusion they need lungs/intestines

why do we have transport systems

as organisms get larger diffusion distance increases so we have transport systems from the specialised exchange surface to where they are needed

what happens in the lungs

exchange oxygen and carbon dioxide

what happens in the small intestine

absorbs nutrients

what happens in the root hair cells

absorb water and mineral ions

common features of all specialised exchange surfaces

• large SA:V ratio

• thin

• partially permeable

• good supply of external medium

features of specialised exchange surfaces in animals

• good blood supply to maintain concentration gradient

why do cells need oxygen

for cellular respiration

how does air move through the lungs

mouth → trachea → bronchi → bronchioles → alveoli

features of alveoli

• one layer of cells thin

• moist to dissolve gases

• large SA:V area

• blood in the capillaries near the alveoli is deoxygenated

breathing rate calculation

rate = breaths/time in mins