Energy transfers in and between organisms

Question 1

Describe the structure of chloroplasts.

Answer 1

-double membrane and the outer membrane is partially permeable to small molecules and the inner membrane regulates passage of large substances
-stroma made of thylakoid membranes which contain lots of chlorophyll and enzymes
-grana are stacks of thylakoids which contain ATP synthase enzymes required to make ATP in light dependent reaction

Question 2

Where does the light dependent reaction take place?

Answer 2

Thylakoid

Question 2

Describe non-cyclic photophosphorylation.

Answer 2

Chlorophyll absorbs light energy which exited electrons to a higher level so that they can leave the chlorophyll as positively charged, it then moves down the electron transport chain releasing energy . The energy transferred from the electrons is used to actively pump H+ ions into thylakoid space creating a proton gradient. Chemiosmosis (movement of hydrogen ions drives ATP synthase )protons move down electrochemical gradient into stroma which phosphorylates ADP to ATP. NADP takes up protons and electrons to form reduced NADP. Photolysis- light causes water to split into protons and electrons and oxygen, electrons are used to replace those lost

Question 2

Give the products of the light-dependent stage of photosynthesis.

Answer 2

-reduced NADP
-oxygen
ATP

Question 3

What is cyclic photophosphorylation?

Answer 3

only used photosystem 1 and involves the excitation of electrons which travel down electron transport chain to release energy to create a proton gradient for chemiosmosis, electrons are not used to reduce NADP but are returned to photosystem 1.

Question 4

What are the products of the light-dependent reaction used for?

Answer 4

to make glucose/sugars/fructose

Question 5

Where does the light independent reaction take place?

Answer 5

The stroma of the chloroplast

Question 6

What products does the light independent reaction require?

Answer 6

Reduced NADP and APT

Question 7

Describe the light independent reaction.

Answer 7

1). Co2 reacts with RuBP to form 6 carbon (6C) molecule which is unstable which dissociates into 2x glycerate 3-phosphate molecules (GP). GP is then reduced to triose phosphate (TP) using reduced NADP and APT from the light dependent reaction. Some TP is converted to organic compounds like glucose though most of the TP is used to regenerate RuBP (5C) using energy form ATP

Question 8

Describe the efficiency of the light independent reaction.

Answer 8

-the light independent reaction has to happen 6 times to make one hexose sugar (glucose)
-three turns of the light independent reaction only produces one molecule of TP

Question 9

How does light intensity effect photosynthesis?

Answer 9

low light intensity limits the light dependent stage of P/S so less ATP and reduced NADP are produced slowing RoR of P/S. Too high light intensity leads to another factor to be limiting and the rate plateaus.

Question 10

How does carbon dioxide effect photosynthesis?

Answer 10

Low CO2 limits the light independent stage as less CO2 is fixed reducing the production of GP and TP. Too high another factor becomes limiting

Question 11

How does temperature effect photosynthesis?

Answer 11

Low temp. provides little kinetic energy slowing the enzyme controlled stages of photosynthesis, like the fixation of CO2 controlled by rubisco, RoR is low. Too high denatures the enzymes so rate of P/S decreases.

Question 12

Why is respiration important?

Answer 12

Respiration produces ATP (to release energy) for active transport and protein synthesis

Question 13

What is an Anabolic reaction?

Answer 13

building larger molecules from smaller molecules, requires energy to make bonds

Question 14

What is a Catabolic reaction?

Answer 14

Breaking larger molecules to form smaller molecules and releases energy as ti breaks bonds

Question 15

Describe the structure of the mitochondria?

Answer 15

-found in eukaryotes
-contains mitochondrial DNA
-Matrix- contains enzymes for the Krebs cycle and the Link reaction
-Intermembrane space- proteins are pumped in by electron transport chain
-Cristae- increase the surface area for oxidative phosphorylation
-Inner mitochondrial membrane- contains electron transport chains and ATP synthase
-Outer mitochondrial- has ideal conditions for aerobic respiration

Question 16

What are the 4 stages of Aerobic respiration?

Answer 16

1). Glycolysis - cytoplasm
2). Link reaction - matrix
3). Krebs cycle - matrix
4). Oxidative phosphorylation - inner mitochondrial membrane of cristae

Question 17

What are the 2 stages of Anerobic respiration?

Answer 17

1). glycolysis - cytoplasm
2). NAD regeneration - cytoplasm

Question 18

What happens in Glycolysis?

Answer 18

Glucose is phosphorylated to glucose phosphate using Pi from 2x ATP which is then hydrolysed to 2 X 3C triose phosphate, which is then oxidised to 2 X 3C pyruvate. the hydrogen is transferred to the co-enzyme NAD to form 2 X reduced NAD and 4 molecules of ATP are produced therefore the net gain of ATP is 2

Question 19

What is the Link reaction?

Answer 19

the 2 molecules of pyruvate are actively transported into the mitochondria and is oxidised and decarboxylated to 2C acetate producing reduced NAD and CO2. Acetate combines with coenzyme A to form Acetyl Coenzyeme A. this happenes twice for every glucose molecule.

Question 20

What is the Krebs cycle?

Answer 20

Acetyl Coenzyme A combines with 4C molecule releasing coenzyme A and producing a 6C molecule which is then decarboxylated and dehydrogenated to a 5C molecule creating CO2 and reduced NAD. 5C molecule is decarboxylated and dehydrogenated to 4C molecule. This process creates APT, 3 molecules of reduced NAD, 1 molecule of FAD and 2 molecules of CO2. occurs twice for every glucose molecule

Question 21

What is Oxidative phosphorylation?

Answer 21

The coenzymes reduced NAD and FAD release hydrogen which splits into protons and electrons, electrons are passed down electron carriers in the inner mitochondrial membrane of the cristae, releasing energy. This energy is used to pump protons from the matrix across the inner membrane creating proton gradient (electrochemical gradient). Protons move back into matrix via ATP synthase which phosphorylated ADP to ATP. The electrons reach the end of the ETC they are passed to oxygen which combines with hydrogen ions which forms water.

Question 22

Describe the efficiency of respiration.

Answer 22

-32% effective
-some ATP is used up moving hydrogen from reduced NAD made during glycolysis into mitochondria
-some is used moving pyruvate in mitochondria via AT
-some energy is used to generate heat

Question 23

Describe how poison effects respiration.

Answer 23

Poison binds to the electron carriers inhibiting the movement of electrons down the ETC which reduces chemiosmosis as proton gradient cannot be established and inhibit the Krebs cycle, reduced NAD and FAD cannot release electron to ETC then they cannot return to the Krebs cycle. ATP production is stopped.

Question 24

Describe how biomass is formed in plants.

Answer 24

During photosynthesis, plants make organic (carbon) compounds from atmospheric or aquatic CO2
● Most sugars synthesised are used by the plant as respiratory substrates
● The rest are used to make other groups of biological molecules (eg. carbohydrates, lipids & proteins) → form biomass

Question 25

How can biomass be measured?

Answer 25

Mass of carbon or dry mass of tissue per given area

Question 26

Describe how dry mass of tissue can be measured.

Answer 26

1. Sample dried in an oven eg. at100 oC (avoid combustion)
2. Sample weighed and reheated at regular intervals until mass remains constant (all water evaporated)

Question 27

Explain why dry mass is more representative than fresh (wet) mass

Answer 27

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

Question 28

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

Answer 28

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

Question 29

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

Answer 29

● Stirrer → evenly distributes heat energy (in water)
● Air / insulation → reduces heat loss & gain to & from surroundings
● Water → has a high specific heat capacity

Question 30

What is gross primary production (GPP)?

Answer 30

● Chemical energy store in plant biomass, in a given area or volume, in a given time
○ Total energy transferred into chemical energy from light energy during photosynthesis

Question 31

What is net primary production (NPP)?

Answer 31

Chemical energy store in plant biomass after respiratory losses to environment taken into account

Question 32

what is the formula for NPP?

Answer 32

NPP = GPP – R
- R = respiratory losses to the environment

Question 33

Explain the importance of NPP in ecosystems.

Answer 33

● NPP is available for plant growth and reproduction
● NPP is also available to other trophic levels in the ecosystem, such as herbivores and decomposers

Question 34

What is primary or secondary productivity?

Answer 34

The rate of primary or secondary production, respectively.

Question 35

State the units used for primary or secondary productivity.

Answer 35

kJ ha-1 year-1 (unit for energy, per unit area, per year)

Question 36

Explain why these units for primary or secondary productivity are used

Answer 36

● Per unit area → takes into account that different environments vary in size
○ Standardising results to enable comparison between environments
● Per year → takes into account effect of seasonal variation (temperature etc.) on biomass
○ More representative and enables comparison between environments

Question 37

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

Answer 37

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

Question 38

State the formula for net production of consumers (N).

Answer 38

N = I – (F + R)
I = the chemical energy store in ingested food
F = the chemical energy lost to the environment in faeces and urine

Question 39

State the formula for efficiency of energy transfer

Answer 39

Energy or biomass available after transfer / energy or biomass available before transfer x 100 if a %

Question 40

Explain why energy transfer between trophic levels is inefficient

Answer 40

● Heat energy is lost via respiration
● Energy lost via parts of organism that aren’t eaten (eg. bones)
● Energy lost via food not digested → lost as faeces
● Energy lost via excretion eg. urea in urine

Question 41

Explain how crop farming practices increase efficiency of energy transfer

Answer 41

● Simplifying food webs to reduce energy / biomass losses to non-human food chains eg.
○ Herbicides kill weeds → less competition (eg. for light) so more energy to create biomass
○ Pesticides kill insects (pests) → reduce loss of biomass from crops
○ Fungicides reduce fungal infections → more energy to create biomass
● Fertilisers e.g. nitrates to prevent poor growth due to lack of nutrients

Question 42

Explain how livestock farming practices increase efficiency of energy
transfer.

Answer 42

● Reducing respiratory losses within a human food chain (so more energy to create biomass):
○ Restrict movement and keep warm → less energy lost as heat from respiration
○ Slaughter animal while still growing / young, when most of their energy is used for growth
○ Treated with antibiotics → prevent loss of energy due to pathogens
○ Selective breeding to produce breeds with higher growth rates