5) Energy Transfer Flashcards
Chloroplasts
Site of photosynthesis
Chlorophyll in thylakoid membrane which is attached to proteins
Protein + pigment= photosystem
2 photosystems used to absorb light energy PSI and PSII
Electron transport chain- formed from photosystems + electron carriers
Stroma surrounds thylakoids
1) Light Dependent reaction of photosynthesis
1) light energy absorbed by PSII- excites electrons in chlorophyll. Chlorophyll photoionised
Electrons have more energy so can move along electron transport chain to PSI
2) Electrons that leave PSII- replaced through photolysis. Light splits water into H+, e- and oxygen.
3) Excited electrons lose energy as they move along the electron-transport chain. Energy used to transport H+ through thylakoid membrane so thylakoid has a higher concentration of H+ than stroma
H+ move down their concentration gradient into stroma via ATP synthase (chemiosomotic theory)
Energy from this combines ADP and phosphate—– ATP
4) Light energy absorbed by PSI- excites electrons to an even higher energy level
Electrons transferred to NADP with a H+ from stroma to form reduced NADP (used in light independent reaction)
2) Light independent reaction of photosynthesis
Calvin Cycle
1) Carbon dioxide diffuses to stroma- reacts with ribulose bisphosphate (RuBP) (5C)
= x2 glycerate 3-phosphate (GP) (3C)
Catalyzed by rubisco
2) Reduced NADP from light dependent reaction- reduces GP to triose phosphate (TP) (3C)
Uses energy supplied by ATP
3) Some TP——- useful organic substances (glucose)
Some TP used to regenerate RuBP (ATP needed)
Environmental factors that limit the rate of photosynthesis
Light
Temperature
Carbon dioxide
Cellular respiration definition
The formation of ATP from the breakdown of glucose
Overview of aerobic respiration
Requires oxygen
1) Glycolysis
2) Link reaction
3) Krebs cycle
4) Oxidative phosphorylation
Anaerobic respiration
X oxygen, produces less ATP
1 stage= glycolysis (same process as in aerobic respiration)
- Pyruvate produced in glycolysis can be converted to ethanol (plants) or lactate (animals) using reduced NAD
- Oxidised NAD produced can be used in further glycolysis
Stage 1 aerobic respiration: Glycolysis
Cytoplasm + produces pyruvate (3C)
1) Glucose phosphorylated- uses 1 ATP. = 1 glucose phosphate (6C) + 1 ATP
2) ATP used to add another phosphate = hexose bisphosphate (6C)
3) Hexose bisphosphate split into 2 triose phosphate (3C)
4) Triose phosphate is oxidized (lose Hydrogen) = 2 pyruvate (3C)- actively transported into matrix of mitochondria for link reaction
5) NAD is reduced by hydrogen atoms = 2 reduced NAD used in oxidative phosphorylation
6) 4 ATP produced, but 2 used up in phosphorylation in earlier stages so net gain of 2 ATP
Stage 2 aerobic respiration: Link reaction
Matrix of mitochondria, no ATP produced
1) pyruvate is decarboxylated (CO2 produced)
2) Pyruvate is oxidized to acetate- producing reduced NAD in the process
3) Acetate combines with coenzyme A (Co A) = acetyl coenzyme A (acetyl CoA)
2 pyruvate molecules are made for every glucose molecule that enter glycolysis. Means that link reaction + Krebs cycle occurs twice for every glucose molecule
Stage 3 aerobic respiration: Krebs cycle
Matrix of mitochondria. Series of oxidation-reduction reactions which generate reduced coenzymes (NAD and FAD) and ATP
1) Acetyl CoA + oxaloacetae (4C) ——— citrate (6C)
2) in a series of oxidation-reduction reactions, citrate loses carbon dioxide and hydrogen to give a 4 carbon molecule
3) ATP produced by direct transfer of a phosphate group to ADP by substrate level phosphorylation
Substrate level phosphorylation= when a phosphate group is directly transferred from one molecule to another
For each molecule of puyruvate, Krebs cycle produces reduced coenzymes (FAD and NAD), 1 ATP, 3 carbon dioxide
Stage 4 aerobic respiration: Oxidative phosphorylation
Energy carried by electrons, from reduced coenzymes, is used to make ATP. Electron transport chain, chemiosmosis
1) Hydrogen atoms released from reduced NAD and reduced FAD as they’re oxidized. H atoms split into protons and electrons
2) Electrons move down electron transport chain, losing energy at each electron carrier
3) Energy is used by electron carriers to pump protons from mitochondrial matrix into intermembrane space
4) Concentration of protons is now higher in intermembrane space than in mitochondrial matrix- electrochemical gradient
5) Protons move down electrochemical gradient, back across inner mitochondrial membrane + into mitochondrial matrix via ATP synthase- movement drives synthesis of ATP from ADP + phosphate
Chemiosmosis= process of ATP production driven by the movement of H+ ions across a membrane
What are the sources of carbon dioxide for plants in ecosystems?
atmospheric or aquatic carbon dioxide
Respiratory substrate definition
a substance required for cellular respiration to derive energy through oxidation
Structure of a food chain or web
Arrows show the direction of energy flow
Producers- photosynthetic organisms
Consumers- obtain energy by feeding on other organisms
Saprobionts- decomposers
Trophic level- each stage of the food chain
Biomass definition
Mass of an organism measured in terms of mass of carbon or dry mass of tissue per given area per given time
Estimating the chemical energy store in dry biomass:
CALORIMETRY
1) Sample dried on oven
2) Sample weighed at regular intervals- once mass becomes constant all water been removed
3) Sample of dry mass is burnt + energy released is used to heat a known mass of water
4) Change of temperature of water is recorded
5) Can calculate how much energy transferred to water + therefore chemical energy of organism
Why do plants only convert a small percentage of the sun’s energy available to them into organic matter?
- Most of sun’s energy is reflected back into space by clouds
- Not all wavelengths of light can be absorbed and used in photosynthesis
- Light may not fall on chlorophyll molecule
Gross primary production (GPP) definition
The chemical energy store in plant biomass, in a given area or volume, in a given time
Net primary production (NPP) definition
The chemical energy store in plant biomass after respiratory losses to the environment have been taken into account
What is NPP available for?
Plant growth, reproduction
other trophic levels in the ecosystem such as herbivores and decomposers
Why is not all chemical energy stored in consumer’s food in animals transferred to the next trophic level?
- Some parts of the organism are not consumed or can not be digested
- Some energy is transferred to the environment by excretory losses and heat from respiration
Equation for net production of consumers (animals)
N = I - (F + R)
N= net production
I= chemical energy in digested food
F= chemical energy lost in faeces and urine
R= energy lost through respiration
Equation for net primary production (plants)
NPP = GPP - R
NPP= net primary production
GPP= gross primary production
R= respiratory losses
Why do most food chains only have 4/5 trophic levels?
- Insufficient energy available to support a large enough breeding population
- Total amount of energy available is less at each level
Equation for efficiency of energy transfer within ecosystems
Efficiency = net production/amount of energy received x100%
Increasing the efficiency of farming:
1) SIMPLIFYING FOOD WEB
Pesticides- kill organisms which reduces amount of energy available for crop growth + therefore NPP
Herbicides- kill weeds so remove direct competition for sunlight
2) REDUCING RESPIRATORY LOSSES
Restricted movement of animals- slower rate of respiration
Indoor pens- warmer- less energy required to generate body heat through respiration.
Means more biomass is produced and more chemical energy can be stored, increasing NPP
Saprobionts definition
a type of decomposer
Secrete enzymes and digest food externally (extracellular division). During this process, organic molecules are broken down into inorganic ions (saprobiotic nutrition)
Objective of nitrogen cycle:
Organisms need nitrogen to make proteins and nucleic acids
Nitrogen cannot be used in its gaseous state
Bacteria convert nitrogen into nitrogen containing compounds that plants can use
Nitrogen cycle:
1) NITROGEN FIXATION
Nitrogen gas is turned into nitrogen containing compounds by bacteria found inside root nodules of leguminous plants
They turn nitrogen to ammonia- forms ammonium ions in solution that can be used by plants
2) AMMONIFICATION
Nitrogen compounds from dead organisms + animal wastes are turned into ammonia by saprobionts which then form ammonium ions
3) NITRIFICATION
Nitrifying bacteria change ammonium ions into nitrites
Other nitrifying bacteria change nitrites into nitrates which can be used by plants
4) DENITRIFICATION
Denitrifying bacteria convert nitrates in soil to nitrogen gas (anaerobic conditions)
Phosphorus cycle:
1) Phosphate ions in rocks- released into soil by weathering. Taken up by plants roots
2) Ions transferred through food chain
3) Transferred to soil through animal waste + products when they die
4) Saprobionts break down organic compounds, release ions to soil
5) Phosphate ions transferred into bodies of water- form sedimentary rock
Mycorrhizae:
When fungi form a symbiotic relationship with roots of a plant
- Fungi form long, thin strands called hyphae- connect to plant root
- Greatly increase SA of plant’s root system
- Helps the plant absorb ions from soil which are scarce + increase uptake of water
- Fungi obtain organic compounds (eg glucose from plant)
How do microorganisms play a vital role in recycling chemical elements in an ecosystem?
- Saprobionts- decomposition of dead animals/faeces (saprobiotic nutrition- process where organic molecules are broken down into inorganic ions)
- Mycorrhizae- facilitate the uptake of water + inorganic ions by plants
- Bacteria in nitrogen cycle- bacteria= nitrogen fixation, ammonification, nitrification, denitrification
Fertilisers + difference between artificial and natural
Used to replace nitrates + phosphates lost by harvesting plants and removing livestock
Cause environmental issues- leaching + eutrophication
Artificial- inorganic, mined from rock
Natural- organic, come from animal remains
Leaching:
- Water soluble compounds in soil from fertiliser are washed away into bodies of water
- Here- may have harmful effect of humans
- Compounds are harmful to environment- eutrophication
Eutrophication:
1) Mineral ions leached from fertilised fields stimulate rapid growth of algae in body of water
2) Blocks light reaching plants below
3) Plants die- unable to photosynthesise
4) Bacteria feed on dead plant matter- bacteria reduce oxygen conc- aerobic respiration
5) Aquatic organisms die- not enough dissolved oxygen
What properties of ATP make it a suitable source of energy in biological processes?
- Energy is released in small + suitable amounts
- Soluble
- Release of energy involves a simple reaction
