Photosynthesis+Class+Notes

__PHOTOSYNTHESIS: AUTOTROPHIC NUTRITION.__ H2O + CO2 -(sunlight + chlorophyl: found in leaf cells)> C6H12O6 (glucose) + O2

Light dependent reaction: light energy is converted into chemical energy, in the form of ATP and NADPH (reducing power because it is a reduction reaction). Must have light, water and chlorophyll to produce ATP + NADPH.

Light independent reaction: CO2 + C6H12O6

Chlorophyll is contained in photosystem 1/ps1 (p700, largest rate of absorption) and photosystem 2/ps2/p680 (major role, reaction centre).

Plant pigments: Chlorophyll a (main pigment) and b: same molecular structure Carotene and Xanthophyll: carotenoid

H2O ---(when light comes in)--> H+ + electron + O

Epidermis: transparent so they have no chlorophyll, allow light to penetrate through. Mesophyll cells in between: contains chlorophyll in chloroplasts so it is green in colour: two layers: top layer is palisade and the lower layer is spongy mesophyll.

Chloroplasts are membrane-bound organelles (thylakoids) with inner and membranes. Chlorophyll is found near the proteins of the membrane.

One electron from ps2 is replaced by the H+ from the water, H+ goes into the lumen of the thylakoid and as the electron is transported along the electron chain, ATP is formed.

when the light energy goes to ps 1, electron shoots out and goes to electron carrier system and forms NADPH, which is transported along the ETC and then, ATP is formed.

outer wall thick and inner wall thin, inner wall expands more, uneven rates of expansion so pumps out water.

electron transport chain: molecules that catch the photons of light plastoquinous b6f complex ferridoxine plastocyanin

**The light reaction involves two groups of pigment:
 * ps1 (p700: wavelength, reaction centre, maximum absorption of light energy, receives light and electrons shoot out and electron is used to synthesise compound called NADPH, which is the reducing power of the recation, ps 1 is replaced by electron from ps1)
 * H2O ---> ps2 --(light)-->ps1 (hole left)--> replaced by electron from water --> NADPH (H comes from the water).
 * LR > ATP and NADPH (two places for ATP: ps 1 and ps 2, and one place for NADPH).
 * ps2 (enough energy to form huge amounts of ATP, water is split into H+ and electron and this is called photolysis: splitting of water; water in the presence of light will split into H+, electron and O): repsonsible for the synthesis of ATP and the photolysis of water such that oxygen is produced

Dark Reactions: Light independent reactions

Light reaction occurs in the membrane of the thylakoid.

Dark reactions take place in the stroma - semi-liquid substance, contains RuBP (Ribulose bisphosphate)-->made up of 5 carbon atoms; receives carbon dioxide to form a 6 carbon compound with two phosphate, unstable (P-6C-P), therefore, it splits into two--> 3C-P (glycerate 3-phosphate) --> takes in another phosphate group from ATP to form ADP-->takes in H from NADPH to form NADP --> glyceraldehyde-p--> can form products such as glucose---> remaining moves back to RuBP to take in more ATP

In order to excite the elctron, huge amounts of light energy is needed.

Seqution of carbon: capturing CO2 from the air and locking it into a product in the form of fuel **IMPORTANT TO KNOW THE IMPORTANCE OF PHOTOSYNTHESIS.**

water plants: air bubbles glowing splint for oxygen test **MUST KNOW WHAT EXPERIMENT TO APPLY FOR WHAT IS NEEDED.** for example, use aquatic plants to see bubbles and see process of photosynthesis taking place.

Red and blue wavelength of light is the spctrum that the plants absorb. The leaves have a spectrum of different colours. Green --> Yellow --> Brown The aquatic plants in submerged in different depths of the water, what colour and wavelength should the plants have? Refractive index of water is different (higher) than that of air so the white light of different colours undergo dispersion at different rates and are slowed down at different speeds.

Mitochondria and chloroplast have their own DNA.

**MUST KNOW HOW TO LABEL CROSS SECTION OF LEAF. AND PARTS OF THE CHLOROPLAST. AND FUNCTIONS OF ORGANELLES.** The pressure is high inside the bark of the tree because the tree has to transport the water from the roots to the other parts of the tree using the xylem tubes in the stem. Aphids just penetrate proboscis into and sucks in water and when there is excess water, it comes out from its anus. Beneficial for ants which can get sugar from the anus.

The top part (pallisade mesophyll) of the mesophyll is saturated with chloroplasts and compact with them - this esnures maximum absorption of sunlight. Packed in horizontal/right angled direction/ perpendicular to upper epidermis - more cells exposed to the sunlight.

Stomata is found in the lower part of the leaf. WHY. Sunlight is not shining on it to increase the rate of evaporation. Temperature lower. When guard cells have choloroplasts, then after photosynthesis, it will have glucose, therefore, there will be an incerase in the osmotic concentration and water potential is decreased. So water goes into the guard cells --> cells become turgid --> inner side of the cell wall thicker and outer side thinner so the outer wall stretches and expands more so make the opening wider --> so when there is no photosynthesis --> osmotic concetration decreases and water potential increases --> cell size reduced and the opening closes. Function - take in air so that the plant can use the carbon dioxide in air. DOES NOT SELECTIVELY TAKE IN CARBON DIOXIDE OR GIVE OUT OXYGEN! When the stomata opens, the air goes in, and water is evaporated out (because the water potential is higher outside the leaf).

Photolysis: using light to break (light dependent stage) water through electrolysis by using the energy from the sun. Oxygen that is produced is from the water molecules. Hydrogen proton is used in the NADPH to generate energy so solar energy is converted into chemical energy, which is needed for the second step (that is why it is needed for the next step).

Carbon fixation: light independent stage

Thylakoid has a lot of membrane so higher surface area - this is where the light dependent reaction takes place so a huge amount of light energy needs to be absorbed.

A-P-P-P: ATP (adenosine triphostphate) ---> when one bond is broken, a huge amount of energy is released --> A-P-P: ADP (adenosine diphostphate) ---> A-P: AMP (adenosine monophostphate) NADP ---> H+ ---> NADPH

Name some features that you think would enable the leaves to be more efficient at photosynthesis?

**Structure** || **Adaptations** || Spongy layer of mesophyll || - Irregular shaped and have large intercellular air spaces, facilitates gas exchange as there are more stomata there, so found in the lower epidermis air spaces allow more air to enter || Lower epidermis has more stomata with guard cells || - Opening in the leaves allow gas exchange: stomata --> required for photosynthesis to take place --> size is regulated by guard cells - found in the lower surface area because it is cut down the water loss through transpiration || Leaves have a large surface area to volume ratio || - leaves are thin (allows gas to pass through, lower and upper epidermis have access to each other) and flat for larger surface area
 * maximizes absorption of sunlight
 * leaf stalk and veins: vascular bundle --> makes the leaf upright and exposed to the surface; leaf is not floppy but firm; provides support
 * vascular bundle --> transports water from roots to the leaves using xylem or the leaf would have to wait for the water from the dew/rain to come which is inefficient
 * xylem is inside and phloem is outside: switch position when it reaches the leaves because of the development ||

Test for starch to see if the plant is photosynthesizing --> plants store products of photsynthesis as starch because glucose increases the osmotic concentration of the cell --> then the cell will become very turgid --> starch is a good storage substance --> it is insoluble (large sized) and immobile; inert because it does not interact with other molecules in the cell

Put in boiling water to kill plant tissues, destroy enzymes and break waxy surface; reaction must be stopped --> put in alcohol/ethanol to to dissolve the phospholipids of the plasma membrane so that the chlorophyll pigment will leak out --> leaf is decolorized easier for colour change to be visible: if it is waxy leaf surface then the iodine will slide off --> submerge in iodine solution

Destarching --> when plant is put in the dark for two days or more

Amount of photosynthesis varies with the intensity of the light. In the light dependent/independent reactions, enzymes are involved (so the graphs are the same!) Saturation point in the intensity of light and the rate of photosynthesis (just like substrate concentration and rate of enzyme activity graph!): limiting factor. How do we increase the limiting factor to increase the saturation point? When there is a greater concentration of caron dioxide. Think of other factors that could be used to increase the limiting factor instead of the light intensity. When the temperature increases by 10 degree celsius, the rate of reaction becomes twice.

Why is heat important? Water molecules bind with enzymes to split into two so that photosynthesis can take place. On a hot day, water molecules are very excited and split fast by binding with the enzymes, so the rate of photosynthesis is high.

When it is too hot? Too much sunlight, tmeperature goes up, the enzymes are denatured because the shape of the active sites are changes and water molecules can no longer bind to them --> plant shrivels up and dies. Maintaining optimum temperature is very important.

Oxygen comes from the water and the light-dependent reaction.