Plant Physiology And Biochemsitry

Question 1

How does gibberellin lead to plant germination

Answer 1

1) seed is dormant
2) seed absorbs water
3) embryo produces Gibberellin
4) gibberellin stimulates aleurone layer
5) to produce amylase
6) amylase hydrolyses starch
7) to endosperm
8) to maltose
9) embryo uses glucose for respiration
10) the energy is then used for growth
11) gibberellin affects transcription of mRNA, coding for amylase

Question 2

Describe the role of ABA in closing the stoma

Answer 2

1) ABA (abriscisic acid) is a stress hormone
2) plant secretes ABA in dry conditions
3) ABA binds to receptors
4) on plasma membrane of guard cells
5) H+ is therefore not pumped out of cell
6) high H+ concentration inside cell
7) k+ diffuses out of cell
8) water potential of cell increases
9) water moves out of cell by osmosis
10) volume of guard cell decreases
11) guard cells become flaccid
12) response is very fast

Question 3

Effect of gibberellin on cell elongation

Answer 3

1) gibberellin is a plant growth regulator
2) this stimulates cell devision and cell elongation
3) cell elongation is due to changes in plasticity of cell wall
4) plant grows tall
5) if you apply gibberellin to drawf plants they will grow taller
6) there are both active and inactive forms of gibberellin
7) drawf plants have the inactive form of gibberellin
8) dominant allele (Le) causes synthesis of enzyme
9) the enzyme catalysed the active form of gibberellin
10) the recessive allele (le) results in the inactive form of gibberellin formed

Question 4

How does gibberellin activate genes

Answer 4

It causes the destruction of DELLA protein repressors, which normally inhibit the transcription Factors that promote the transcription of the alpha amylase gene

Question 5

How does auxin control cell elongation

Answer 5

1) Auxin binds to auxin receptor proteins in CSM
2) ATPase proton pump, pumps H+ from the cytoplasm into the cell wall
3) ph decreases
4) expansins (proteins) in cell wall are activated and break bonds between cellulose microfibrils and surrounding substances
5) cellulose microfibrils can move past each other temporarily
6) cell can expand while cell wall remains fairly strong
7) auxin also stimulates opening of potassium ion channels
8) k+ diffuses into cytoplasm and lowers water potential
9) water diffuses into cell by osmosis through aquaporins
10) cell wall stretches and elongates

Question 6

How do Venus fly traps close

Answer 6

1) sensory hairs are touched twice in quick succession
2) h+ ions are pumped out of midrib cells into cell wall
3) high h+ concentration lowers ph
4) calcium pectate (the glue) in the cell walls dissolve
5) cell walls of mid rib cells loosen
6) high h+ concentration outside midrib cells create an electrochemical gradient
7) ca2+ diffuse into the midrib cells which lowers water potential causing water to enter
8) midrib cells expand
9) lobes flips from convex to concave
10) trap closes

Question 7

When is ATP and reduced NADP used in photosynthesis

Answer 7

It is used in the light independent stage (calvin cycle) of photosynthesis to produce complex organic compounds

Question 8

Where is the sight of the light dependent stage of photosynthesis

Answer 8

Thylakoid membrane

Question 9

Where is the sight of the light independent stage of photosynthesis

Answer 9

Stroma

Question 10

What pigments are in the chlorophylls group

Answer 10

These are the primary pigments and include chlorophyll a which absorbs yellow-green light. As well as chlorophyll b which absorbs blue-green light

Question 11

What pigments are in the carotenoids group

Answer 11

These are the accesory pigments and includes beta carotene which absorbs orange light. As well as xanthphyll which absorbs yellow light.

Question 12

What is the role of photosynthetic pigment

Answer 12

They absorb certain wavelengths of light, light energy is needed in photolysis.

Question 13

Absorption spectrum

Answer 13

A graph of the absorbance of different wavelengths of light by pigment. It shows that little green light is absorbed, as this light is then reflected back the leaf appears green

Question 14

Action spectrum

Answer 14

A graph of the rate of photosynthesis at different wavelengths of light. This shows the effectiveness of the different wavelengths of light, which is related to their absorption and their energy content. The shorter the wavelength the greater the energy it contains.

Question 15

Retention factor equation

Answer 15

Distance travelled by pigment / distance travelled by solvent

Question 16

Chromatography

Answer 16

You crush the leafs in a solvent. A mixture of pigments extracted from leafs is placed on the paper at the pencil line, it is dabbed on by capillary tube and given time to dry before more leaf extract is added. You then put the paper in a beaker with some solvent which is just below the pencil line. The solvent rises up the paper carrying each pigment at a different speed. This separates the pigment as they move at different speed.

Question 17

Light independent reaction

Answer 17

Carbon dioxide from the atmosphere diffuses into the leaf through stomata and diffuses into the palisade mesophyll cells and then into the stroma of the chloroplast. In the stroma, carbon dioxide combines with the five carbon compound (ribulose biphosphate) RuBP using the enzyme RUBISCO. The combination of carbon dioxide and RuBP produces a 6-carbon compound which is unstable and breaks down into two molecules of the 3-carbon compound (glycerate 3-phosphate) GP. ATP and reduced NADP from the light dependent reaction are used to reduce the activated GP to (triose phosphate) TP. Some TP molecules are converted to useful organic substances such as glucose. Most TP molecules are used to regenerate RuBP using ATP produced from the light dependent reaction

Question 18

Cyclic photo-phosphorylation

Answer 18

Involves only photosystem 1. Light is absorbed by photosystem 1 and is passed to the primary pigment. An electron in the chlorophyll molecule is excited to a higher energy level and is emitted from the chlorophyll molecule. It is captured by an electron acceptor and passed back to the chlorophyll molecule via a chain of electron carriers. Enough energy is released to synthesise ATP from ADP and inorganic phosphate by chemiosmosis. ATP is used in the light independent reaction

Question 19

Non-cyclic photo-phosphorylation

Answer 19

Involves both photosystems. Light is absorbed by both photosystems and excited electrons are emitted from the primary pigment of both reaction centres. Theses electrons are absorbed by electron acceptors and pass along chains of electron carriers. The primary pigment of photosystem 1 absorbs electrons from photosystem 2. Its primary pigment receives replacement electrons from photolysis. ATP is synthesised as the electrons loose energy whilst passing along carrier chains

Question 20

Photolysis of water

Answer 20

In photosystem 2, an enzyme cause H2O -> 2H+ + 2e- + 1/2O2. Oxygen is a waste product which is used by the plant in aerobic respiration, or released through the stomata. The protons are used to reduce NADP with electron from inorganic phosphate

Question 21

The hill reaction

Answer 21

Liquidise the leaves in ice cold water and filter the resulting suspension to remove unwanted debris. Chill small tubes of buffered chloroplast suspension. Add DCPIP solution to the tubes. Place the tubes in different light intensities. Assess the blue colour at 1 minute intervals. Record the rate of loss of blue colour using a colourimeter

Question 22

overview of light dependent reaction

Answer 22

Light energy excites electrons in the chlorophyll molecule in the thylakoid membrane, causing them to pass to an electron acceptor at the start of the electron transport . Electrons pass down the chain from one electron carrier to the next in a series of redox reactions. This process generates ATP from ADP and inorganic phosphate in a process called photophosphorylation. Light splits water into protons (H+ ions), electrons and oxygen (waste). The electrons are used to replace the electrons lost from the chlorophyll in step 1. This process is called photolysis of water. The protons are pumped across the membrane using the ATP in a process called chemiosmosis. This creates a chemical potential gradient. Reduced NADP is generated as the electrons in the electron transport chain are transferred to NADP along with a proton. Protons pass back through the membrane through an ATP synthase enzyme which makes ATP. Approximately 4 protons make one ATP molecule. Both ATP and reduced NADP are used in the light-independent stage of photosynthesis.

Question 23

How are C4 plants adapted to their role

Answer 23

RuBP in bundle sheaf cells, away from oxygen to avoid photorespiration. Carbon dioxide combines with PEP, it is catalysed by PEP carboxylase in mesophyll cells. This forms oxaloacetate which is converted to malate. Malatate passes to bundle sheath cells, it then releases high concentrations of carbon dioxide. RuBP then reacts with the carbon dioxide. The enzymes also have a high optimum temperature

Question 24

What happens to the calvin cycle intermediates

Answer 24

Some TP condenses to form hexose phosphate which is used to produce starch for storage, sucrose for translocation, or cellulose for making cell walls. Others are converted to glycerol and fatty acids to produce lipids for cellular membranes. Or the production of amino acids for protein synthesis

Question 25

Limiting factors

Answer 25

The factor which is nearest its lowest value and is thus limiting the reaction. This occurs when a process is affected by more then one factor.

Question 26

Factors which affect the rate of photosynthesis

Answer 26

Light intensity and wavelength, temperature and carbon dioxide concentration

Question 27

How light intensity affects rate of photosynthesis

Answer 27

The rate of photosynthesis increases with increasing light intensity. However, at a high light intensity the rate of photosynthesis plateaus as it is no longer the limiting factor

Question 28

The effect on the rate of photosynthesis of varying the temperature at constant light intensities

Answer 28

At high light intensity the rate of photosynthesis increases as the temperature is increased over a limited range. At low light intensity, increasing the temperature has little effect on the rate of photosynthesis, as the light intensity is now the limiting factor.

Question 29

The effect of carbon dioxide on photosynthesis

Answer 29

At constant light intensity and temperature, the rate of photosynthesis initially increases with increasing carbon dioxide concentration, but reaches a plateau at higher concentrations.

Question 30

Growing plants in protected environments such as grennhouses

Answer 30

An understanding of environmental factors helps farmers to increase the rate of photosynthesis and ultimately the yield. In glasshouses, sensors can monitor the light intensity, the humidity of the atmosphere and the concentration of carbon dioxide around the plant. It can then adjust them so that they are their maximum amount. Plants can be grown hydroponically ie their roots are in a nutrient solution, whose nutrient content can be varied at different points of growth. Pesticide can be added

Question 31

How can you alter light intensity

Answer 31

By altering the distance of a small light source

Question 32

How can you alter wavelength of light

Answer 32

By using different colour filters, making sure they transmit the same light intensity

Question 33

How can you alter concentration of carbon dioxide

Answer 33

By adding different quantities of sodium hydrogencarbonate (NaHCO3) to the water surrounding the plant this reduces CO2 concentration

Question 34

How can you alter temperature

Answer 34

Using a large container to help maintain the chosen temperature, use a heater or ice

Question 35

How do you investigate the rate of photosynthesis

Answer 35

The aquatic plant such as elodea needs to be well illuminated before it is cut and put in the test tube. In order that the gases don’t dissolve in the water, the water needs to be well aeriated ie you bubble air through it.

Question 36

Structure and function of the chloroplast

Answer 36

The membranes of the grana provide a large surface area, which hold the pigments, enzymes and electron carriers needed for the LDR. The membranes mean that a large number of pigment molecules can be arranged so that they absorb as much light as possible. The pigments are arranged in funnel like structures, each pigment passes energy to the next member of the cluster, finally passing it to the chlorophyll a reaction centre. The stroma contains the enzymes needed in the LIR.

Question 37

Why do organisms need energy

Answer 37

To synthesise complex substances from simpler ones ie polysaccharides, DNA replication or protein synthesis. Maintenance of constant body temperature. The active transport of substances ie the sodium potassium pump. Mechanical work such as muscle contraction

Question 38

ATP

Answer 38

Is the universal energy carrier and provides an immediate source of energy for cellular processes. There is not a lot of ATP in the body because it is an immediate between energy yielding and energy requiring processes. It is suited for this role as it is readily hydrolysed to release energy, it is also small and water soluble

Question 39

Synthesis of ATP

Answer 39

Some ATP is synthesised by reorganising chemical bonds (chemical potential energy) during glycolysis and the krebs cycle. Most ATP is generated using electrical potential energy by transferring electrons in chloroplast and mitochondria

Question 40

Chemiosmosis

Answer 40

Protons diffuse down the concentration gradient, through a protein channel by facilitated diffusion to get across the phospholipid bilayer. Part of the protein channel acts as the enzyme ATP synthase. The ATP synthase has three binding sites and part of the molecule rotates as hydrogen ions pass through. Each proton facilitates three different phases as the molecule rotates. The first phases binds ADP and inorganic phosphate, the second phase forms a tightly bound ATP and the third phase releases ATP.