17+18 - Energy for biological processes & respiration Flashcards
The need for energy
Growth, response, make/find food, reproduce, predation……
These all require metabolic activities:
Active transport (uptake of nitrates by plants, loading sucrose into sieve tube cells and conduction of nerve impulses)
Anabolic reactions (building polymers like proteins, polysaccharides)
Movement (cillia, flagella or contractile filaments in muscles)
photosynthesis
carbon dioxide + water → glucose + oxygen
6CO2 + 6H2O → C6H12O6 + 6O2
Occurs in 2 stages
Aerobic Respiration
glucose + oxygen → carbon dioxide + water + ATP
C6H12O6 + 6O2 → 6CO2 + 6H2O + ATP
Occurs in 4 stages
energy and bonds
- energy is used to break bonds
- energy is released when bonds are formed
how does respiration release energy
- large organic molecules break down to form small inorganic molecules
- the energy to break the bonds is less than the energy released in the formation of al the bonds in the smaller inorganic products
- excess energy released is used to synthesis ATP
explain how breaking down glucose & fatty acids can release energy when bond breaking is an endothermic process.
- carbon and hydrogen are equal in EN, so have non-polar bonds
- so bond doesn’t require lots of energy to break
- C and H break and form new bonds with oxygen, releasing energy
How does ATP release its energy?
- ATP has 3 phosphate groups, so is fully “charged”
- A small amount of energy is used to break the 3rd phosphate from the ATP
- A large amount of energy is released due to interactions involving the products (especially the phosphate making new bonds)
-ADP can be “recharged” via respiration by adding another phosphate group back
Chemiosmosis:
-Diffusion of protons from a region of high concentration to a region of low concentration through a partially permeable membrane.
Uses a PROTON (H+) concentration gradient
-> The movement of protons as they flow down CG releases energy that is used for attachment of ADP + Pi ATP
How is the proton gradient created? in chemiosmosis
The energy needed to create the gradient comes from high-energy electrons – excited electrons.
Electrons are raised to higher energy levels in 2 way:
-> Electrons in pigments e.g. chlorophyll are excited by absorbing sunlight.
-> High energy electrons are released when chemical bonds are broken in respiratory substrates e.g. glucose.
The excited electrons pass into an electron transport chain in the mitochondria and are used to generate a proton gradient.
Electron transport chain
- Series of electron carriers (protein complexes), each causing electrons to drop to lower energy levels.
- As high energy electrons move down energy levels, energy is released.
- This is used to pump protons across the inner membrane, from the matrix into the intermembrane space, creating a concentration gradient.
ATP synthase
- Protons can only move back through membrane channels linked to the enzyme ATP synthase. (facilitated diffusion)
- The flow of protons through the channels provides energy to synthesise ATP.
- This whole process, including the ETC, is called “Oxidative phosphorylation”
explain the importance of ATP to living organisms
-Universal energy currency
-energy transfer is, quick/immediate
-energy is in, small/usable, quantities
-(energy transfer) is quick,
-(energy transfer) in quantities that can be used
-ATP can be resynthesised
describe the properties of cell membranes necessary for the formation of a proto gradient
-Impermeable to, ions/protons
-idea that there can be different concentrations of protons on each side of a membrane
-contains, embedded / integral, proteins
e.g., ATP synthase
enzyme responsible for synthesis of ATP
what type s diffusion is proton movement at ATP synthase and explain the role of ATP synthase
Facilitated diffusion
-ATP synthase provides hydrophilic channel for diffusion of protons
- catalyses the synthesis of ATP (1); lowers activation energy
Most ATP is produced in mitochondria by chemiosmosis.
Outline how ATP is produced in mitochondria by chemiosmosis
idea of establishment of H+ ion gradient
-> pumping protons into intermembranal space’
H+ ions, flow down a concentration gradient /
from intermembrane space to matrix
through ATP synthase
energy, provided / AW, to join ADP and Pi ( to form ATP)
Heterotroph
Organisms that acquire nutrients by the ingestion of other organisms
Autotroph
Organisms that synthesise complex organic molecules from inorganic molecules. (they make their own food)
Photoautotrophs
Organisms that can photosynthesise – use energy from sunlight to make complex organic molecules from inorganic molecules (CO2 and H2O)
structure and function of chloroplasts
- PHS is here
- large network of membrane = large SA for maximum absorption of light
- flattened thylakoids stack to form grana, joined by lamellae
-light is absorbed by complexes of pigments which are embedded in thylakoid membrane - fluid in the chloroplast is called stroma and is the site of chemical reactions
Photosynthetic pigments
Molecules that absorb light energy.
Found embedded in the thylakoid membrane.
Each pigment absorbs a range of wavelengths in the visible region and has its own distinct peak of absorption.
Other wavelengths are reflected or transmitted.
Chloroplast’s main pigment is chlorophyll a
They however also contain accessory pigments.
These include chlorophyll b, carotenoids like carotene, and xanthophylls to broaden their effectiveness in absorbing visible light
How do pigments work?
Pigments are arranged in photosystems.
Photosystems can be divided into 2 regions, The antennae complex (or light harvesting complex) & the reaction centre.
Accessory pigments in the antennae complex transfer light energy to the primary pigments in the reaction centre.
chlorophyll a
Chloroplast’s main pigment
There are 2 types of chlorophyll a – P680 and P700 named so because of their absorption peaks.
Each have a different photosystem:
Photosystem I (PSI)
Photosystem II (PSII)
Photosystem II (PSII)
chlorophyll a - P680
primary pigment absorbs light at 680nm so is known as P680
Photosystem I (PSI)
primary pigment absorbs light at 700nm so is known as P700
a chlorophyll a - P680 and P800 different chlorophyll molecules
They contain IDENTICAL chlorophyll a molecules. It is their association with different proteins which affects their electron distribution in the chlorophyll molecules and accounts for the slight differences in light absorbing properties.
Stages of photosynthesis
- what it needsm where to and what is it doing
Light dependent reactions
->Needs light
->Takes place in the thylakoid membranes
->Light energy is converted to chemical energy - ATP (using the photosystems) and NADPH2
Light Independent reactions
->Does not use light directly
->Takes place in the stroma
-> Where glucose is made using the ATP and NADPH2 from the light dependent reaction
Non-cyclic Photophosphorylation
1. Light travels in parcels of energy called call ‘photons’
- When a photon hits chlorophyll in PSII, two electrons become excited
3 Excited electrons are captured by electron acceptors and passed along a series of electron carriers within the thylakoid membrane
- Energy is released as the electrons are pass along the electron transport chain
5. This pumps H+ ions across the thylakoid membrane into the thylakoid lumen – creating a concentration gradient
- The H+ ions flow down a gradient across channels associated with ATP synthase enzymes
- ATP synthase drives the formation of ATP from ADP and Pi
8.This is called chemiosmosis
Photolysis of water
The electrons lost from the chlorophyll in PSII must be replaced to continue the flow of electrons along the electron transport chain.
Within the thylakoid space, an enzyme splits water (photolysis) using energy from the Sun, to give oxygen gas, hydrogen ions and electrons.
The electrons replace those that were emitted from the reaction centre of PSII.
The hydrogen ions contribute to the proton gradient across the thylakoid membrane
The Oxygen gas is released by the plant as a waste product
Reduction of NADP
Electrons are excited again by light at PSI and electrons pass along another (very short) electron transport chain (This does not pump any H+ across the membrane, it is just used to transfer the electrons to the next stage).
Ultimately, they combine with the coenzyme NADP and hydrogen ions from the water to form reduced NADP (aka NADPH).
Cyclic Photophosphorylation
If ATP is needed, but not NADH, thylakoids can carry out “Cyclic Photophosphorylation”.
In this process electrons leave PSI, moved to the second electron transport chain, then returned to the first ETC.
The Electrons are used to pump H+ ions across the membrane before being returned to PSI where they are excited by light again. This process repeats, generating the H+ gradient that allows ATP to be produced, but prevents NADPH from being generated.
Light independent reaction
Photolysis of water
Non-cyclic Photophosphorylation
Reduction of NADP
Describe two ways in which the structure granum is adapted to its function.
contain, (named) pigment (molecules) / photosystems;
contain, (named) electron carriers / ETC / ATP synth(et)ase;
idea that has a large surface area (in a small volume) for, light absorption / light dependent reaction(s) / light dependent stage / electron transport;
Name the primary photosynthetic pigment in photosystems I and II.
chlorophyll, a / A;
Name an accessory pigment.
chlorophyll b / xanthophyll(s) / carotenoid(s) / (β / beta-) carotene;
State the advantage to the plant of having a range of accessory pigments in photosystems.
able to, absorb / use,
a range of / different / more / other,
(light) wavelengths / λ
Name the compound that is synthesised in the light-dependent stage as a result of the generation of an electrical and pH gradient across the thylakoid membrane.
ATP
Limiting factors
a factor that limits the rate of a process when at a lower level
Light Intensity – explaining to A level standard
- As light intensity increases, the rate of photosynthesis will increase (as long as other factors are in adequate supply)
2 As the rate increases, eventually another factor will come into short supply and increase in rate of PHS slows
3 Eventually, even if light intensity is increased, rate of PHS doesn’t change (plateau)
Low light levels mean less ATP and reduced NADP. This slows down the Calvin cycle (conversion of GP to TP and RuBP).
No light = none of this.
Light is also needed for photolysis
Increased light means more ATP and reduced NADP, meaning more photolysis, more LDR and therefore more LIR
Temperature - explaining to A level standard
Affects rate of enzyme controlled reactions… each step in PHS is dependent on enzymes (ATP synthase, NADP reductase, RuBisCO…)
At lower temp, substrate molecules have less kinetic energy which means there will be fewer successful collisions and a slower rate of reaction… lower conc of GP, TP, RuBP. Slower enzymes mean a slower Calvin cycle.
At a certain point, enzymes will be denatured (irreversible) and PHS will ultimately stop! Hot temperature stop the Calvin cycle.
However, the rate of photorespiration also increases above 25oC, meaning that even if enzyme is not denatured, rate of PHS might be limited by an increase in photorespiration!
High temperatures also cause more water loss from stomata, leading to the stress response of closing. Less carbon dioxide can then access the plant… closely linked to CO2 as a limiting factor
plant Uses of glucose
Used in respiration
Converted to starch; storage tubers
To make complex carbohydrates; xylem phloem, cell walls
To make amino acids. Enzymes
Build fats and oils eg nuts
The Calvin Cycle
The cyclical light independent reactions of photosynthesis
Carbon fixation
The incorporation of CO2 into organic molecules
RuBisCO
An enzyme used in photosynthesis, carries out carbon fixation in the Calvin cycle (very inefficient, thought to be the most abundant enzyme in the world). Short for “Ribulose bisphosphate carboxylase/oxygenase”.
Ribulose Bisphosphate (RuBP)
A 5-carbon organic molecule.
