Topic 5 Energy & eco systems

Question 1

Describe how biomass is formed in plants

Answer 1

During photosynthesis, plants make organic carbon compounds from atmospheric or aquatic CO2. Most sugars made are used by the plant as respiratory substrates.
The rest of the sugars are used to make other groups of biolgoical molecules such as carbs, lipids and proteins which form biomass

Question 2

How can biomass be measured?

Answer 2

Mass of carbon or dry mass of tissue per given area

Question 3

Describe how dry mass of tissue can be measured and why the factors at each stage are as they are

Answer 3

Sample dried in oven at 100 degrees to avoid combustion
The sample is weighed and reheated at regular intervals until the mass remains constant so all the water has evaporated.

Question 4

What is biomass

Answer 4

Biomass is the total mass of living material in a specific area at a given time

Question 5

Explain why dry mass is more representative than fresh wet mass?

Answer 5

Water volume in wet samples will vary but not affect the dry mass

Question 6

Describe how the chemical energy stored in dry biomass can be estimated?

Answer 6

Using calorimetry:
-Known mass is biomass is fully combusted (burnt)
-Heat energy released heats a known volume of water
-Increase in temperature of the water is used to calculate chemical energy of the biomass

Question 7

Explain how features of a calorimeter enable valid measurement of heat energy released

Answer 7

Stirrer- Evenly distributes heat energy in water
Air/insulation- reduces heat loss and gain to and from surroundings
Water- has high specific heat capacity

Question 8

What is gross primary production?

Answer 8

The total quantity of chemical energy stored in plant biomass in a given area or volume in a given time. It is also the total energy transferred into chemical energy from light energy during photosynthesis.

Question 9

What is net primary production?

Answer 9

The amount of chemical energy stored in plant biomass after some energy is lost to respiration

Question 10

State the formula for net primary production

Answer 10

Gross primary production - respiratory losses = net primary production

Question 11

Explain the importance of net primary production in ecosystems

Answer 11

The net primary production is available for plant growth and reproduction, it is also available to other trophic levels in the ecosystem such as herbivores and decomposers

Question 12

What are the units used for primary or secondary productivity?

Answer 12

kJ m-2 year-1 (unit for energy per unit area per year)

Question 13

What is primary or secondary productivity?

Answer 13

The rate of primary or secondary production, respectively

Question 14

Why are the given units for primary or secondary productivity used?

Answer 14

kJ- amount of energy produced
Per unit area- takes into account that different environments vary in size which standardizes results to enable comparison between environments.
Per year- Takes into account the effect of seasonal variation (e.g temperature) on biomass. This is more representative and enables comparison between environments.

Question 15

Explain why most light falling on producers is not used in photosynthesis

Answer 15

-Light is reflected or wrong wavelength
-Light missed chlorophyll/chloroplasts/photosynthetic tissue
-CO2 concentration or temperature is a limiting factor

Question 16

State the formula for net production of consumers

Answer 16

N=I-(F+R)
N- net production
I- ingested food
F- Energy lost in urine and faeces
R -represents the energy lost in respiration

Question 17

State the formula for efficiency of energy transfer

Answer 17

Percentage efficiency transfer = biomass in higher trophic level / biomass in lower trophic level × 100

Question 18

Explain why energy transfer between trophic levels is inefficient

Answer 18

-Heat energy is lost via respiration
-Energy lost via parts of organism that aren’t eaten e.g bones
-Energy lost via food not digested like faeces
-Energy lost via excretion e.g urea in urine

Question 19

Explain how different crop farming practices increase efficiency of energy transfer

Answer 19

You can simplify the food webs to reduce energy/biomass loss to non human food chains such as Herbicides-Kill weeds so there is less competition(e.g light) so more energy to create biomass
Pesticides- Kill insects to reduce loss of biomass from crops from eating the crops (in direct competition with humans) or damaging crops and reducing ability to photosynthesize thus reducing productivity
Fungicides- Reduces fungal infections which means crops have more energy to create biomass.
Fertilisers- e.g. nitrates to prevent poor growth due to lack of nutrients due to lack of nutrients.

Question 20

Explain how livestock farming practises increase efficiency of energy transfer

Answer 20

Reducing respiratory losses within a human food chain
-Restrict movement and keep warm so less energy is lost as heat from respiration and vasodilation(most reared species are warm blooded)
-Slaughter animals while growing/young when most of their energy is used for growth
-Treat with antibiotics to prevent loss of energy to fighting pathogens
Selective breeding to produce breeds with higher growth rates

Question 21

Explain the role of saprobionts in recycling chemical elements

Answer 21

-Decompose organic compounds such as proteins and DNA in dead matter
-Secreting enzymes for extracellular digestion
-Absorb soluble needed nutrients and release mineral ions e.g. Phosphate ions

Question 22

Explain the role of mycorrhizae

Answer 22

Symbiotic association between fungi and plant roots Fungi acts as an extension of plant roots to increase surface area of root system
This increases rate of uptake/absorption of water and inorganic ions#In return fungi receive organic compounds e.g carbohydrates

Question 23

Give examples of biological molecules that contain nitrogen

Answer 23

Amino Acids
Proteins/Enzymes
Urea
DNA RNA
Chlorophyll
ATP/ADP
NAD/NADP

Question 24

What are the 4 main stages of the nitrogen cycle

Answer 24

Ammonification
Nitrification
Nitrogen fixation
Denitrification

Question 25

Describe the stage of ammonification in the nitrogen cycle

Answer 25

NItrogen containing compounds such as proteins and urea from dead organisms are broken down/decomposed. Saprobiontic micro organisms mainly fungi and bacteria that feed on this(release enzymes for extracellular digestion) release ammonia which then forms ammonium ions in the soil.

Question 26

Describe the stage of nitrification in the nitrogen cycle

Answer 26

Ammonium ions in the soil are converted from ammonium ions to nitrite ions (NO2-) then from nitrite ions to Nitrate ions (NO3-) via a 2 step oxidation reaction. This reaction is carried out by nitrifying bacteria in aerobic conditions (oxygen), this is an exothermic reaction

Question 27

Describe what nitrogen fixation is and the process

Answer 27

Nitrogen gas is converted into nitrogen containing compounds, it can be carried out industrially or when lightning is struck. There is free living nitrogen fixing bacteria that reduce gaseous nitrogen to ammonia which these use to manufacture amino acids In addition, there is mutualistic nitrogen fixing bacteria that live on root nodules in plants like peas/ beans they obtain carbohydrates from the plant and the plant amino acids from the bacteria

Question 28

Describe the process of denitrification

Answer 28

When nitrates in soil are converted into nitrogen gas through reduction reaction by denitrifying bacteria in anaerobic conditions (e.g.waterlogged soil)

Question 29

Suggest why ploughing (aerating soil) increases its fertility

Answer 29

More ammonium converted into nitrite and nitrate (more nitrification) Less nitrate converted to nitrogen gas (less denitrification)

Question 30

Give examples of biological molecules that contain phosphorus

Answer 30

Phospholipids/DNA RNA/ ATP or ADP

Question 31

Describe the phosphorus cycle

Answer 31

Phosphate ions in rocks are released into soils and oceans by erosion Phosphate ions are taken up by producers and incorporated into their biomass(rate of absorption increased by mycorrhizae) Phosphate ions are transferred through food chain e.g producers are eaten by herbivores Some phosphate ions lost from animals in waste products Saprobionts decompose organic compounds like DNA in dead matter releasing phosphate ions

Question 32

Explain why fertilisers are used

Answer 32

To replace nitrates and phosphates lost when plants are harvested and livestock are removed. Those removed from soil and incorporated into biomass cant be released back into soil through decomposition by saprobionts. So efficiency of energy transfer is improved increasing yield

Question 33

Describe the difference between artificial and natural fertilisers

Answer 33

Natural fertilisers- Organic matter that consists of dead and decaying remains e.g. manure. Ions from these fertilisers are released during decomposition by saprobionts Artificial fertilisers- Inorganic fertilisers that are mined from rocks and deposits, converted into different forms and blended for appropriate balance of minerals. NPK always present.

Question 34

Explain the key environmental issue arising from use of fertilisers

Answer 34

Phosphates and nitrates dissolve in water leading to leaching of nutrients into lakes. This leads to eutrophication which is where there is an algal bloom so light is blocked. Submerged plants die as they cannot photosynthesise. Saprobionts decrease dead plant matter using oxygen in aerobic respiration. There is less oxygen for fish to aerobically respire leading to their death

Question 35

Explain the key advantage of using natural fertiliser over artificial fertiliser

Answer 35

-Less water soluble so less leaching and eutrophication is less likely -Organic molecules require breaking down by saprobionts which means there is slow release of nitrate/phosphate

Question 36

What are the stages of photosynthesis and where do they occur

Answer 36

-Light dependent reaction in the thylakoid membrane of chloroplast -Light independent reaction of stroma of chloroplast

Question 37

Describe photoionisation in the light dependent reaction

Answer 37

-Chlorophyll absorbs light energy which excites electrons to a high energy level -Electrons are released from chlorophyll so chlorophyll becomes positively charged

Question 38

Describe the stage after photoionisation in the light dependent reaction

Answer 38

Some energy released from electrons in photoionisation is conserved in the production of ATP/Reduced NAPD which is called the chemiosmotic theory which is where: -Electrons move along electron transfer chain releasing energy -This energy is used to actively pump protons from the stroma into thylakoid -Protons can move by facilitated diffusion down electrochemical gradient into stroma via ATP synthase channel proteins which form small granuels on the membrane surface known as stalked granuels -As protons pass through these ATP synthase channels they cause changes to the structure of the enzyme which the catalyses the combination of ADP with inorganic phosphate to form ATP

Question 39

Describe the photolysis of water in the LDR

Answer 39

Light strikes chlorophyll molecule leaving it short of electrons and unable to absorb light Water splits to reduce protons, electrons and oxygen, Electrons replace those lost from chlorophyll. The protons produced pass out of the thylakoid space through ATP synthase channels and are taken up by NADP. This reduces NADP to become reduced NADP which enters the light independent reaction.

Question 40

Describe the light independent reaction of photosynthesis (calvin cycle)

Answer 40

-CO2 diffuses into leaf through stomata and dissolves in water around the walls of mesophyll cells. Then diffuses into stroma of the chloroplast where it reacts with ribulose bisphosphate (RuBP) catalysed by the enzyme rubisco -This forms 2 glycerate 3-phosphate (GP) molecules -Reduced NADP from light dependent reaction is used to reduce GP is reduced to Triose phosphate (TP) using energy supplied by ATP. -Reduced NADP is re-formed and goes back to the light dependent reaction to be reduced again by accepting more protons -Some TP converted to useful organic substances (e.g. glucose) -Some TP used to regenerate RuBP in the calvin cycle using energy from ATP

Question 41

Describe and explain how temperature affects the rate of photosynthesis

Answer 41

1) As temperature increases, rate increases -Enzymes such as rubisco gain kinetic energy so more enzyme substrate complexes are formed 2) Above optimum temperature, rate decreases -Enzymes denature as H bonds in tertiary structure break -Fewer enzyme substrate complexes form

Question 42

Describe and explain how light intensity affects rate of photosynthesis

Answer 42

1) As light intensity increases, the rate increases -Light dependent reaction increases do there is more photoionisation of chlorophyll so more ATP and reduced NADP produced. -Light independent reaction increases as more GP reduced to TP and more TP regenerates RuBP 2) Above a certain light intensity, the rate stops decreasing, this is because another factor is limiting such as Temp or CO2 conc

Question 43

Describe and explain how CO2 concentration affects the rate of photosynthesis

Answer 43

1) As CO2 conc increases, rate increases -Light independent reaction increases -More CO2 combines with RuBP to for GP -So more GP reduced to TP -So more TP converted to organic substances and more RuBP regenerated 2) Above a certain CO2 concentration, rate stops increasing because of other limiting factors such as temp/ light intensity

Question 44

Explain the key consideration when evaluating data relating to agricultural practices used to overcome the effect of limiting factors

Answer 44

Agricultural practice should increase the rate of photosynthesis leading to increased yield because, more glucose produced for faster respiration so more ATP release energy for growth e.g cell division and protein synthesis. But extra profit from extra yield should be greater than costs.

Question 45

Describe how pigments from a leaf of a plant can be isolated with paper chromatography

Answer 45

-Crush leaves with solvent to extract pigments -Draw a pencil line on chromatography paper 1cm above bottom -Add a drop of extract to line (point of origin) -Stand paper in boiling tube of organic solvent below the point of origin -Add lid and leave to solvent to move up carrying dissolved pigments -Remove before solvent reaches top and mark solvent front with a pencil

Question 46

Explain why the origin should be drawn in pencil rather than with ink

Answer 46

Ink is soluble in solvent so it would mix with the pigments causing the line to move

Question 47

Explain why the point of origin should be above the level of the solvent

Answer 47

Pigments are soluble in solvent, so would run off paper

Question 48

Explain why a pigment may not move up the chromatography paper in one solvent

Answer 48

May be soluble in one solvent but insoluble in another

Question 49

Describe how pigments can be identified from chromatogram

Answer 49

Calculate Rf value which is = distance moved by spot/distance moved by solvent front -Compare Rf value to published value

Question 50

Explain why the solvent front should be marked quickly once chromatography paper is removed

Answer 50

Once solvent evaporates, solvent front is not visible

Question 51

Explain why the centre of each pigment spot should be measured

Answer 51

Standardises readings as pigment is spread out. this allows comparisons to be made

Question 52

Explain why the obtained Rf values were similar but not identical to the published values

Answer 52

DIfferent solvent/paper/running conditions may affect Rf value

Question 53

Explain why Rf values are used and not the distances moved by the pigment spots

Answer 53

Solvent/pigment moves different distances. Rf value is constant for the same pigment so value can be compared

Question 54

Describe the role of the enzyme dehydrogenase in photosynthesis

Answer 54

-Catalyses the reduction of NADP in the light dependent reaction -NADP accepts electrons from photoionisation of chlorophyll/ photolysis of water

Question 55

Describe how the rate of dehydrogenase activity in extracts of chloroplasts can be measured

Answer 55

-Extract chloroplasts from a leaf sample using centrifuge -Control 1 - set volume of DCPIP (redox indicator dye, electron acceptor), water and chloroplasts in isolation medium, covered in foil to block light B. Control 2 - set volume of DCPIP, water and isolation medium without chloroplasts C. Standard - set volume of water and chloroplasts in isolation medium, without DCPIP D. Experiment - set volume of DCPIP, water and chloroplasts in isolation medium Shine light on test tubes and time how long to it takes for DCPIP to turn from blue (oxidised) to colourless (reduced) in tube D (tube A and B should show no change) - Compared to a colour standard (tube C) to identify end point 4. Rate of dehydrogenase activity (1/time taken)

Question 56

What is a limit to the method to measure dehydrogenase activity and how can this be overcame?

Answer 56

-End point (colour change) is subjective -Use a colorimeter -Measure light absorbance of the sample at the set time intervals -Zero colorimeter using the colour standard

Question 57

why respiration is important ?

Answer 57

-Respiration produces ATP which is used for active transport and protein synthesis

Question 58

Summarise the stages of aerobic and anaerobic respiration

Answer 58

Aerobic- 1. Glycolysis - cytoplasm (anaerobic) 2. Link reaction - mitochondrial matrix 3. Krebs cycle - mitochondrial matrix 4. Oxidative phosphorylation - inner mitochondrial membrane Anaerobic respiration 1) Glycolysis- cytoplasm 2) NAD regeneration- cytoplasm

Question 59

Describe the process of glycolysis

Answer 59

-Glucose phosphorylated to glucose phosphate using inorganic phosphates from the hydorlysis of 2 ATP -Glucose phosphate is hydrolysed to 2x triose phosphate -Each molecule is oxidized to pyruvate and the 2 lost hydrogens are transferred to Hydrogen carrier molecule NAD -2 NAD reduced to for Reduced NAD -Enzyme controlled reactions convert each triose phosphate into another 3 carbon molecule called pyruvate. In the process, net increase of 2 ATP molecules regenerated

Question 60

Explain what happens after glycolysis if respiration is anaerobic

Answer 60

-Pyruvate is converted to lactate (in animals and some bacteria) or ethanol (in plants and yeast) -Oxidising reduced NAD- NAD regenerated -SO glycolysis can continue (which needs NAD) allowing continued production of ATP

Question 61

Suggest why anaerobic respiration produces less ATP per molecule of glucose than aerobic respiration

Answer 61

-Only glycolysis involved which produces little ATP (only 2 molecules) -No oxidative phosphorylation which forms majority of ATP (34 molecules roughly)

Question 62

What happens after glycolysis if respiration is aerobic?

Answer 62

Pyruvate is actively transported into the mitochondrial matrix.

Question 63

Describe the link reaction in respiration

Answer 63

-Pyruvate molecules are actively transported from the cytoplasm to the mitochondrial matrix -Pyruvate is oxidized to acetate by releasing CO2 and 2 hydrogens -and reduced NAD produced as NAD accepts hydrogens -Acetate combines with coenzyme A, forming Acetyl coenzyme A

Question 64

Describe the Krebs cycle

Answer 64

1) Acetyl coenzyme A reacts with a 4C molecule -releasing coenzyme A -producing a 6C molecule that enters the Krebs cycle -In a series of reactions the 6C molecule looses CO2 and hydrogen to regenerate the 4C molecule and a single molecule of ATP as a result of substrate level phosphorylation (direct transfer of pi from intermediate compound to ADP). -For each molecule of pyruvate, the Link reaction and Krebs cycle produce: -reduced co enzymes NAD and FAD -One molecule of ATP 3 molecules of CO2

Question 65

Describe the process of oxidative phosphorylation

Answer 65

-The hydrogen atoms produced during glycolysis in the krebs cycle combine with the coenzymes NAD & FAD -The now reduced NAD & FAD are oxidised to release H atoms which are split into H+ protons and electrons (e-) 2) Electrons transferred down the electron transfer chain by redox (say oxidation reduction) reactions 3) Energy released by electrons used in the production of ATP from ADP+Pi (chemiosmotic theory) and used by electron carriers to actively pump protons from matrix -Protons diffuse into matrix down an electrochemical gradient via ATP synthase -Releasing energy to synthesise ATP from ADP and PI 4) In a matrix at end of electron acceptor, oxygen is the final electron acceptor, so protons, electrons and oxygen combine to form water.

Question 66

Describe how lipids can be used as a respiratory substance instead of glucose

Answer 66

-Lipids are first hydrolysed to glycerol and fatty acids -Glycerol is then phosphorylated and converted to triose phosphate which enters the glycolysis pathway -Fatty acids broken down into 2 carbon components and converted to acetyl coenzyme A.

Question 67

Describe how a respirometer can be used to measure the rate of aerobic respiration

Answer 67

Add a set mass of a single celled organism e.g yeast to a set volume/concentration of substrate e.g glucose. Add a buffer to keep pH constant. Add a chemical that absorbs CO2 e.g. sodium hydroxide Place in water bath at a set temperature and allow to equilibrate Measure distance move by coloured liquid in a set time

Question 68

In aerobic respirometer, why does the liquid move?

Answer 68

-Organisms aerobically respire and take in o2 -Co2 is given out but absorbed by sodium hydroxide solution -So volume of gas and pressure in the container decrease -So fluid in capillary tube moves down a pressure gradient towards organism

Question 69

Explain why the aerobic respirometer apparatus is left for 10 minutes

Answer 69

-Allow apparatus to equilibrate -Allow for overall pressure expansion/change throughout -Allow respiration rate of organism to stabilise

Question 70

Explain why the apparatus must be airtight for aerobic respirometer

Answer 70

To prevent air entering or leaving, this would change volume and pressure affecting movement of liquid

Question 71

Describe a more accurate way to measure a volume of gas

Answer 71

Use a gas syringe

Question 72

Describe how a respirometer can be used to measure the rate of anaerobic respiration

Answer 72

You need to measure CO2 release -You repeat aerobic experiment but remove chemical that absorbs co2. -Then you make conditions anaerobic by e.g. Layer of oil to stop O2 diffusing in/ Add a chemical that absorbs O2/ Leave for an hour to allow O2 to be respired and used up

Question 73

Why would the liquid move in the anaerobic respirator test?

Answer 73

-Yeast respires anaerobically to release CO2 -Volume of gas and pressure in a container increase -Fluid in capillary tube moves down a pressure gradient away from organism

Question 74

Explain why the apparatus is left for an hour after the culture has reached a constant temperature in anaerobic respirometer experiment

Answer 74

To allow time for oxygen to be used/respired

Question 75

Describe how redox indicator dyes such as methylene blue can be used to measure rate of respiration

Answer 75

-REdox indicators such as this change colour when they accept electrons becoming reduced -Redox indicators take up hydrogens and get reduced instead of NAD/FAD modelling their reactions

Question 76

Describe the adaptations of a leaf that allow it to engage in photosynthesis

Answer 76

-Large SA that absorbs as much sunlight as possible -An arrangement of leaves on the plant that minimise overlapping to avoid shadowing of one leaf by the other -Thin as most light absorbed and short diffusion distance -A transparent cuticle and epidermis that let light through to the photosynthetic mesophyll of cells beneath -Long, narrow upper mesophyll cells packed with chloroplasts that collect sunlight -Numerous stomata for gaseous exchange -Many airspaces in the lower mesophyll to allow rapid diffusion -Network of xylem that brings water to the leaf cells and phloem that carries away the sugars produced during photosynthesis.

Question 77

What are the products of the light dependent reaction vs the light independent reaction

Answer 77

Light dependent- NADP, ATP and Oxygen Light independent- Sugars and other organic materials

Question 78

How are chloroplasts adapted for their function in the LDR

Answer 78

Thylakoid membrane- Large SA for the attachment of chlorophyll, electron carriers and enzymes that carry out the light independent reaction Network of proteins in the grana- Hold the chlorophyll in a very precise manner that allows max absorption of light Grana membranes- Have ATP synthase channels within them which catalyse the production of ATP, they are also selectively permeable which allows establishment of proton gradient Chloroplasts contain both DNA and ribosomes so they can quickly and easily manufacture some of the proteins involved in the light dependent reaction

Question 79

How are chloroplasts adapted to their function in the LDR

Answer 79

-Fluid of the stroma contains all enzymes needed to carry out the light independent reaction. Stromal fluid is membrane bound in the chloroplast which means a chemical environment which has a high concentration of enzymes & substrates can be maintained -The stroma fluid surrounds the grana and so the products of the LDR in the grana can quickly diffuse into the stroma -Contains both DNA and ribosomes so it can manufacture proteins

Question 80

Explain how the Krebs cycle performs an important role in the cells of organisms

Answer 80

-Breaks down macromolecules into smaller ones (Pyruvate broken down into CO2) -Produces H atoms that are carried by NAD to the electron transfer chain and provides energy for oxidative phosphorylation which leads to production of ATP for cell metabolic energy -It regenerates the 4C molecule which combines with acetylcoenzyme A, otherwise, it would accumulate -Source of intermediate compounds used by cells in the manufacture of other important substances such as fatty acids, amino acids and chlorophyll

Question 81

Explain how protein can be used as a respiratory substance instead of glucose

Answer 81

-Protein is first hydrolysed into amino acids -They have their amino acid group removed before entering the respiratory pathway -3- carbon compounds are converted to pyruvate 5- carbon compounds are converted to intermediates in the krebs cycle