Unit 3.3 Understanding Photosynthesis

Oxygen is a product of-

Photosynthesis

All living things must get their energy from what original source?

The sun

Do living things get their energy from the sun directly or indirectly?

Both. Plants get it directly, we get it from plants indirectly through eating organic carbon-containing compounds like sugars made by plants

What 2 benefits would we get by maximizing conditions and reactions for photosynthesis?

Higher crop yields and better nutritional food value

What does “photosynthesis” mean?

“Making with light”

Define photosynthesis

Process where light energy is captured and channeled into the production of food molecules

What is the chemical formula for photosynthesis?

6CO₂ + 6H₂O + Light Energy → C₆H₁₂O₆ +6O₂

Plants use light energy to make-

Carbohydrates

What type of photosynthesis does this course focus on? 3 things

Green, O₂ producing, eukaryotic plants

Define chloroplast

Organelle in plants where photosynthesis occurs

Where on the plant are chloroplasts?

In the green leaves; the cells just below the epidermal layer; seen in the palisade and spongy mesophyll cells

What do chloroplasts look like?

Small abundant circles, like a mini cell with an outer membrane

Define thylakoid and what is embedded within it

Stacks of membranous disks in the chloroplast; embedded with proteins

Define granum (singular)

Thylakoids grouped into columns

Define lumen

The internal thylakoid environment

Define lamellae

Flat bands of ribbon-shaped membrane that connects thylakoids from different grana (plural)

Define stroma

Aqueous medium where other structures are suspended in

Define chlorophyll. Where it is?

A structure containing special light-sensitive pigments; inside the chloroplast and bound to the membranes of the thylakoid

What thing makes the chloroplast green and gives it its light-absorbing capability?

Chlorophyll

What are the names of the two main forms of chlorophyll?

a and b

What is the structural difference between Chlorophyll a and Chlorophyll b?

Chlorophyll a has a methyl functional group and Chlorophyll b has a carbonyl functional group (think AM and BC)

Chlorophyll a and b belong to a group of molecules called what?

Pigments

What do pigments do?

They absorb light energy at specific electromagnetic wavelengths depending on the pigment’s colour mostly within the visible spectrum

What are 2 examples of accessory pigments?

1. Carotenoids

2. Xanthophylls

Why are plants green?

Chlorophyll a and b absorb light at the blue/violet and red wavelengths and reflect green light wavelengths!

Can both Chlorophyll a and b absorb the energy and transfer the electrons for photosynthesis?

No, only a. Chlorophyll b and accessory pigments can absorb energy and pass electrons to a so that a wider range of light energy can be harvested

Define “action spectrum”

“Sum total of the absorption of light energy by all the pigments in plants.” Entire range of visible light wavelengths can be captured. All colours are absorbed and green is reflected

What are the names of the 2 stages of photosynthesis?

1. Light-dependent reactions/Light reactions

2. Light-independent reactions/Dark reactions/Calvin Cycle

Do light-dependent reactions/light reactions require light?

Yes

In simple terms, where are the NAMES of the 3 steps of stage 1 light-dependent reactions?

1. Capture of light energy

2. Transfer of light energy by intermediate energy carriers

3. Transformation of light energy into chemical potential energy → ATP and NADPH

What is the antenna system?

Association of several chlorophyll a and carotenoids

What are the names of the 2 different arrangements of pigments/proteins connected with the antenna system and reaction centre?

1. Photosystem II (680)

2. Photosystem I (700)

Recall- what is the Electron Transport Chain (ETC)?

A metabolic pathway where an electron enters a carrier complex, is transferred, passed from carrier to another protein complex via redox reactions

What are ATP and NADPH?

Two kinds of energy-containing molecules made by the energy in the photons of light captured by chlorophyll

ATP is produced after which photosystem?

Photosystem II

NADPH is produced after which photosystem?

Photosystem I

What is non-cyclic photophosphorylation?

Means that the electrons donated by chlorophyll a are never returned to it. Electrons are accepted by NADP to form NADPH. Donated electrons must be replaced- done so by electrons being stripped from H₂O

What is cyclic-photophosphorylation and in whom does it occur?

Occurs in photosynthetic bacteria; electrons donated by chlorophyll a are returned to it via the ETC. ONLY ATP is generated from the H⁺ proton gradient- no free electron to attach to NADP⁺ so no NADPH made. Loop that cycles electrons between photosystem I and the ETC

How can energy be both used and stored? What is it stored as?

When glucose is produced, it can either be used immediately to release energy/provide the raw materials to build cell wall. Often more glucose is made than is needed so the extra is stored as starch.

What are the names of the 3 different types of photosynthesis?

1. C₃, C₄, and CAM

What is cool about C₃ and C₄?

They can adapt to less optimal temperatures for photosynthesis by managing/preventing photorespiration

What is photorespiration?

Process that reduces the efficiency of photosynthesis, like preventing it when unfavourable temperatures are present

Photorespiration occurs when-

plants try to conserve water loss when temperature is too high

When photorespiration increases, what decreases?

Efficiency of plants to convert sunlight into food

Between C₃ and C₄, which is better at higher temperatures and which is better at lower?

C₃ is better at lower temperatures; C₄ is better at higher temperatures

What conditions lead to photorespiration?

At high temperatures, leaves lose water by evaporation through openings in the leaves called stomata. Stomata closes to conserve water BUT O₂ builds up inside the leaves and CO₂ can’t enter. Leads to photorespiration

Most plants in the world are which type?

C₃ at 95%

Describe C₄ plants

Plants that fix carbon onto molecules containing 4 carbon atoms

What are CAM plants?

A plant that can cope in hot/dry climates. Limit photorespiration by doing C₄ pathways at night and Calvin Cycle during the day.

What is temporal separation?

Reversing the timing of stomatal openings

Describe how stomata (plural) open and close

Stomata are pores on the surface of leaves that allow CO₂ in and O₂ out. Can be opened and closed by the plant. Most plants keep stomata open during the day to absorb CO₂ and closed at night to prevent water loss

What is a big difference between C₄ and CAM plants?

To survive in hot climates, C₄ performs spatial isolation meaning there’s a higher concentration of CO₂ in different cells. In CAM plants, temporally isolate CO₂ within the same cell day vs. night

What thing absorbs energy from red and blue wavelengths from light and transfers the electrons required for photosynthesis?

Chlorophyll a

What thing absorbs energy from red and blue wavelengths from light and pass them through the antenna complex to chlorophyll a?

Chlorophyll b

Xanthophylls and Carotenoids absorb light wavelengths that chlorophyll a and b cannot. They pass the energy to absorb to chlorophyll a via the antenna complex. What are they?

“Other pigments”

“Process of combining the carbon atoms from carbon dioxide into a glucose molecule is called-”

Fixing the carbon

Light-dependent reaction: transfer of light energy by intermediate energy carriers