Week 4

Question 1

Where does photosynthesis occur?

Answer 1

Chloroplasts. In the leaf mesopyll cells (the middle layer of the leaf).

Question 2

define photosynthesis.

Answer 2

the conversion of light energy into chemical energy in the form of organic compounds. Performed by plants, algea, and some prokaroyotes.

Consists of two stages:
-the light reaction
-the calvin cycle

CO2 is the oxidizing agent, and becomes reduced

H2O is the reducing agent, and becomes oxidized

Question 3

What are chloroplasts and what are their different parts?

Answer 3

Where photosynthesis occurs in eukaroyotic cells.

Thylakoids: membrane bound compartments

Stroma: the fluids surrounding the thylakoids

Granum: stacks of thylakoids

the light reaction occurs in the thylakoids, while the calvin cycle occurs in the stroma.

Question 4

what are pigments?

Answer 4

substances that absorb visible light of specefic wavelengths. The colour that we see is the one colour that is least absorbed by that pigment.

Question 5

What are the photosynthetic pigments and their roles?

Answer 5

Contain three main types of pigments in their thylakoid membranes.

Chlorophyll a: the primary light capturing pigment

chlorophyll b: accessory pigment, that works together with chlorophyll a

carotenoids: broaden the spectrum of light that can drive photosynthesis (the greater percentage of the light visible spectrm can be used for photosynthesis) and for photoprotection (helps to absorb and dissapate excess energy that would otherwise harm the cekks).

Question 6

What is the action spectrum?

Answer 6

how well different wavelengths of light support photosynthesis.

Question 7

Why do leaves change colour in the autumn?

Answer 7

the chlorophyll pigments degrade
AND

the caretnoids (orange and yellow) being the dominant pigments, so they won’t get abosrbed and instead show that colour.

Question 8

What is the light reaction?

Answer 8

converts solar energy into chemical energy, the part that is directly dependent on sunlight.

Transfers electrons and protons from water to NADP+ to form NADPH.

Produces ATP from ADP through an electrons transport chain and chemiosismosis in photophosphorylation.

This also does not produce any sugars, this is done in the calvin cycle.

Question 9

How is solar energy captured in the light reaction?

Answer 9

Captured by photosystems. Two types are photosystem II and photosystem I.

Solar energy is capturned by exciting electrons to a higher orbital.

Question 10

Role of photosystem II?

Answer 10

an excited electron is captured by the primary electron acceptor.

Question 11

What is the linear electron flow summary?

Answer 11

1 H2O + 1.5ADP +1.5 Phosphate + 1 NADP+ + light -> 0.5O2 + 1.5ATP + 1NADPH + H+

Question 12

What are the key differnces between photophosrylation and oxidative phosphorylation?

Answer 12

Photo:
- electrons pumped across thylakoid membrane, and high concentration of protons in the thylakoid space
-electrons come from water
-the final terminal electron acceptor is NADP+

Oxidative:
-electrons pumped across the inner mitochondiral membrane, resulting in high concentration of protons in the intermembrane space
-electrons come from organic molecules (NADH and FADH2)
-the final terminal electron acceptor is O2

Question 13

What is the calvin cycle?

Answer 13

Uses the ATP and the NADPH produced in the light reaction to generate G3P (a sugar). Glucose is not a direct product of photosynthesis, but G3P is later converted into glucose.

It takes three turns of the cycle to produce one G3P molecule.

Consists of three stages:
-carbon fixation
-reduction
-regeneration of RuBP

Question 14

What is the carbon fixation stage of the calvin cycle?

Answer 14

the first stage of the calvin cycle.

it is the initial incorporation of CO2 into an organic molecule and performed by rubisco. Rubsico is the most abundant enzyme on earth. Will add the CO2 to rubisclose biphosphate and will form short lived intermediates that will break down into two molecules of 3-phosphate glycerate.

Question 15

What is the reduction stage of the calvin cycle?

Answer 15

The second stage of the calvin cycle.

Energy from ATP and electrons from NADPH are used to reduce 3-phosphoglycerate to form G3P molecules (which can later be changed to make glucose)

Question 16

What is the regeneration stage of RuBP for the calvin cycle?

Answer 16

The third and final stage of the calvin cycle.

The molecule that starts the cycle is regenrated for future cycles.

Question 17

What is the overall final equation for the calvin cycle process?

Answer 17

3CO2 + 6NADPH + 9ATP + 5H2) -> 1G3P + 6NADP+ + 9ADP + 8Phosphate +2H+

(keep in find that the NADPH, CO2, and ATP were generated in the light reaction)

Question 18

Do plants need oxygen to survive?

Answer 18

yes and no. plants need to perform cellular work and need ozygen for that, but they produce more oxygen than they require, and dont need oxygen from other places for this.

Question 19

What are the two types of cell signalling?

Answer 19

Local and long distance.

Question 20

What does local signalling include?

Answer 20

Direct contact via cell junctions and cell-cell recognition. This could involve protein receptors on one cell reckognizing surface proteins or carbohydrates on another cell.

Signal molecules act on local cells (could be many cells) or specific target (only detected by one other).

Question 21

What is paracrine signalling?

Answer 21

the secretition of signal molecules detected by nearby cells

Question 22

Long distance Signalling?

Answer 22

communication of cells located in different parts of the organism. Based on the secretion and detection of signalling molecules known as hormones produced by both plants and animals.

this is known as endocrine signalling in animals.

Question 23

What are the 3 stages of cell signalling?

Answer 23

1. Reception (cells detect the presence of a signal)
2. Transduction (the signal is converted into a form that can bring about cellular change)
3. Response (the final cellular change that is brought as a result to the signal)

Question 24

Describe Reception.

Answer 24

requires a receptor protein with the correct binding site to reckognize a signalling molecule.

Signalling molecules acts as ligands (which are molecules that speceifically bind to another, often larger molecule) whose binding impacts the shape and function of the receptor, which activates it.

Receptors can be cell surface (plasma membrane) or intracellular (cytoplasm or nucleus).

Question 25

What are cell surface receptors? Explain the different types.

Answer 25

These are integral membrane proteins (which means they are embedded within the plasma membrane).

Three main types exist:
-G protein-coupled receptors (GPCRs)
-Receptor Tyrosine Kinase (RTKs)
-Ligand-gated ion channel receptors

Question 26

G protein coupled Receptors (GPCRs)

Answer 26

work with a G-protein that binds GDP/GTP. spefificity for both signal molecules and type of G protein.

in the inactive site the G-protein is not associated with a single molecule. binding causes the receptor to change shape, and the change in shape causes the receptor to interact with the G protein, resulting is GDP being replaced by GTP (and this replacement activates the G protein). Once activated and binded, diffuses along the membrane and iteracts with its target enzyme. This interaction causes a change in shape for the enzyme which impacts its function, either activating it or inhibiting it. Once completed, returns back to its inactive state.