Topic 5

Question 1

What is an ecosystem

Answer 1

the interaction between living organisms an the environment in a given area

Question 2

What is a habitat

Answer 2

The place is here an organisms lives with a fistic set of conditions

Question 3

What is a niche

Answer 3

The role that s species has in a community

Question 4

Outline succession

Answer 4

The first organism to colonise bare rival are lichens or algae- there are the only species that can cope with the harsh conditions
the pioneer specis start to break the rock surface allowing some

Question 5

what are anthropogenic factors

Answer 5

these are factors which arise from human activity this can either be abiotic or biotic

Question 6

outline the light dependent stage

Answer 6

1. light energy is absorbed by the PSII
2. the light energy excites the electrons in chlorophyll
3. the electrons move to a higher energy level PSI along the electron transport chain
4. the electrons that left the PSII need to be replaced so PHOTOLYSIS ( the splitting of water) this will then produce H+ and electrons
5. as the electrons go to higher energy levels they lose energy
6. this energy is used to move the H+ form the stoma to the thylakoid membrane through ATP synthase (by facilitated diffusion as H+ are charged molecules)
7. the H+ ions move down the conc gradient, the energy from this is used to combine ADP and Pi to make ATP
8. the co enzyme NADP takes to H+ to form NADPH

Question 7

outline the light independent reaction

Answer 7

1. co2 diffuses into the storm of the chloroplast
2. it combines with ribulose niphopshate RuBP this is catalysed by the enzyme RUBISCO
3. this forms an unstable 6 carbon compound, and then it breaks down into two molecules of a 3 carbon compound glycerate-3 phosphate GP
4. the ATP from the light dependant reaction provides energy for the the GP to turn into GALP (which is also a 3 carbon compound)
5. before this reaction can take place it requires H+ ions provided by NADPH+ (from the light dependant reaction) then the NADP goes back to the light depart reaction to pick up more H+
6. once GALP is formed it it converted into useful organic compounds such as glucose
7. some of the GALP is needed to go back to RuBP and this uses the rest of the ATP from the light dependant reaction

Question 8

how can dendrochronology be used to as evidence fro climate change

Answer 8

tress produce one tree ring a year
the thickness of this ring depends on the climate
if ut is thicker then the climate was warmer
the cores of the tree trunks are taken then date each ring by counting back from when the core was taken
by looking at the thickness they can see what the climate was like each year

Question 9

how can peat bogs be used as evidence for climate change

Answer 9

pollen is usually preserved in peat bogs (which is acidic)
peat bogs accumulate in layers so the pollen will be preserved in layers
the cores of the peat bogs will be taken and then the pollen will be analysed
if the pollen in the layers of the peat bigs are similar to the species of pollen in the current climate that mean that climate has not differed that much from when that pollen was made
however if it has differed then the climate has changed
additionally pollen from a specific species of plant that thrives in warmer conditions will suggest that the climate has changed

Question 10

how can temperature records be used as evidence of climate change

Answer 10

since the 1850s the temperature record have been kept but initially they were obtained using thermometers, this may mean that the data collected may not be as reliable

Question 11

describe the structure of the chloroplast

Answer 11

they have a double membrane called the chloroplast envelope
they contain thylakoids which have a large surface area which allows a lot of light to be absorbed for photosynthesis
they are stacked up into structures called grana/granum
the storm contains the enzymes, sugars and organic acids required for photosynthesis

Question 12

what the effects of climate change

Answer 12

1. the change in rainfall pattern
   some areas may gate more rainfall whereas others may get less - this will affect the development of life cycles in some organisms, this will affect the DISTRIBUTION of the species
2. seasonal cycles
   it wil change the timing of the seasons - this will affect the development of life cycles of some organisms
   and change the distribution of these species

Question 13

how does the carbon cycles help to reduce atmospheric co2

Answer 13

CARBON in the form of co2 is absorbed plants when they carry out photosynthesis and it is turned into CARBON COMPOUNDS
CARBON is then passed on to animals when they eat plants and to decomposers hone they eat dead organic matter
carbon is returned to the atmosphere as the living organisms carry out respiration where it is released as co2

Question 14

allopatric speciation

Answer 14

a geographical barrier will cause a population to separate
in each side of the geographical barrier there will be different conditions and different selection pressures
this will cause different changes in the alley frequency
some alleles will be more advantageous, this will then cause these ones with the advantageous alley to survive
then they will reproduce snd then pass on this advantageous allele
the allele frequency will increase
then these species will become so different that they cannot produce fertile offspring
and therefore become different species

Question 15

sympatric speciation

Answer 15

there will be variation in the alleles of the species due to mutations
there will be some alleles that are better adapted to the environment
this with the advantageous allele are more likely to survive and pass on this advantageous allele
there is an increase in the allele frequency

Question 16

Core practical 4: Investigate the effect of enzyme and substrate concentrations on the initial rates of reactions.

Answer 16

Combine a dilute stock solution of trypsin with distilled water to produce solutions with concentrations of 0.2%, 0.4%, 0.6% and 0.8%.
1. Make a control by adding 2cm3 of trypsin solution and 2cm3 of distilled water. Use this to set the colorimeter absorbance to zero.
2. To another cuvette, add 2cm3 of milk suspension and 2cm3 of the stock trypsin solution. Mix, place in the colorimeter and measure absorbance at 15 second intervals for 5 minutes.
3. Rinse the cuvette with distilled water.
4. Repeat step 3 at all trypsin concentrations.
Rate of reaction= 1/ mean time

Question 17

Core practical 10: Using quadrats and transects to determine distribution and abundance of organisms, and measuring abiotic factors appropriate to the habitat.

Answer 17

1. Choose a site where there is an obvious gradient in an abiotic variable. Place the transect down. Select a species that changes in abundance along the gradient.
2. Place the quadrat at each of the marks on the transect, placing the bottom left corner on the mark every time.
3. Record the percentage cover for the chosen species. This can be done by recording how many of the quadrat’s 100 squares contain the chosen species. A square should only be counted if half or more of it is covered.
4. At each coordinate, a measure of the independent variable should be taken. For example, if investigating light intensity, a photometer can be used to take a reading for the light intensity at each coordinate.

Question 18

Core Practical 11: Investigate photosynthesis using isolated chloroplasts (the Hill reaction).

Answer 18

1. Remove stalks from leaf samples. Cut into small sections. Grind sample using a pestle and mortar and place into a chilled isolation solution. - Cold to prevent enzyme denaturation and enzyme activity
2. Place several layers of muslin cloth into a funnel and wet with isolation medium to filter sample into a beaker.
3. Suspend the beaker in an ice water bath to keep sample chilled.
4. Transfer to centrifuge tubes and centrifuge at high speed for 10 minutes. This will separate chloroplasts into the pellet.
5. Remove supernatant and add pellet to fresh isolation medium.
6. Store isolation solution on ice.
7. Set the colorimeter to the red filter. Zero using a cuvette containing chloroplast extract and distilled water.
8. Place test tube in rack 30cm from light source and add DCPIP. Immediately take a sample and add to cuvette.
9. Measure the absorbance of the sample using the colorimeter
10. Take a sample and measure its absorbance every 2 minutes for 10 minutes.
11. Repeat for different distances from lamp up to 100 cm. This will vary the light intensity.

NB: This experiment should be done in a darkened room to make results more reliable. The sample should not be put too close to the lamp as temperature may affect results.

Question 19

Core practical 12: Investigate the effect of temperature on the rate of an enzyme-catalysed reaction, to include Q10.

Answer 19

1. Grind a known mass of peas in distilled water and place in a boiling tube.
2. Add 5cm of hydrogen peroxide solution to the peas.
3. Fit the syringe into a delivery tube and the delivery tube into the boiling tube with a bung. 4. Place the boiling tube into a water bath at a known temperature.
4. Time for a set length of time e.g. 5 minutes. Measure the volume of gas produced at regular intervals e.g. 30 seconds.
5. Repeat the experiment at different temperatures.