Plant and Photosyntheis

What is the cell wall in plant cells?

A rigid outer layer made mainly of cellulose that provides structure

What is the central vacuole?

A large, fluid-filled organelle that occupies most of the plant cell

What are the functions of the central vacuole?

Stores water, ions, and waste

What are plasmodesmata?

Microscopic channels connecting adjacent plant cells

What is the function of plasmodesmata?

Allow transport and communication between cells

What is the phragmoplast / cell plate?

A structure formed during plant cell division that develops into a new cell wall.

What is the role of the cell plate in cytokinesis?

It forms between two daughter cells and grows outward to divide the cell

Cellulose microfibrils

Strong fibers (main support)

Hemicellulose

Links fibers together

Pectin

Sticky gel (glues cells)

Lignin

Hardens + waterproofs

Cell wall layers (simple)

Plasma → Primary → Middle

Full layers (with secondary)

Plasma → Secondary → Primary → Middle

Primary cell wall composition

Cellulose + hemi + pectin

Primary cell wall properties

Thin + flexible

When is primary wall made?

During growth

Primary wall growth method

Acid growth

Secondary cell wall composition

Cellulose + hemi + lignin

Secondary cell wall properties

Thick + rigid

Middle lamella composition

Pectin

Middle lamella function

Glues cells together

Tonoplast

Vacuole membrane

Tonoplast function

Controls movement in/out of vacuole

Transvacuolar strands

Cytoplasm strands through vacuole

Function of transvacuolar strands

Move materials across cell

Why no cleavage in plants?

Rigid cell wall

Phragmoplast function

Builds cell plate

Shape of phragmoplast

Barrel-shaped

Phragmosome

Cytoplasm layer (division plane)

Where does cell plate form?

In phragmosome

Cell plate role

Divides cell

What are plastids?

Organelles for photosynthesis and storage

Where did plastids evolve from?

From ancient cyanobacteria

From ancient cyanobacteria

Green plastids that perform photosynthesis

Green plastids that perform photosynthesis

Make and store pigments (colors)

What are leucoplasts?

What are leucoplasts?

What do amyloplasts store?

Store starch (energy reserve)

What do elaioplasts store?

Store fats (lipids)

Store fats (lipids)

Store proteins

How are plastids categorized?

Based on color and function

Chloroplast envelope membranes

Double membrane surrounding the chloroplast

Outer membrane

Permeable to small molecules

Intermembrane space

Space with no clear function

Inner membrane

Selective barrier controlling entry/exit

Stroma

Fluid inside; site of Calvin cycle

Stroma properties

Protein-rich and slightly alkaline

Granum (grana)

Stacks of thylakoids

Thylakoid

Membrane sac for light reactions

Thylakoid function

Contains light-dependent reaction proteins

Thylakoid space (lumen)

Acidic interior of thylakoid

Lamella

Connects grana stacks together

What happens to water in light reactions?

Split to release O₂ and electrons

Where do light-dependent reactions occur?

Thylakoid membrane

Calvin Cycle purpose

Uses ATP/NADPH to make glucose

What does the Calvin Cycle fix?

Carbon (CO₂ → glucose)

Where does the Calvin Cycle occur?

Stroma

What do pigments do in photosynthesis?

Absorb light energy for photosynthesis

Chlorophyll a

Main pigment; blue-green; transfers energy

Role of accessory pigments

Expand light range + protect from damage

Chlorophyll b

Accessory pigment in green plants

Phycoerythrin

Red pigment

Carotenoids

Fat-soluble pigments for protection

Carotenes

Orange pigments

Xanthophylls

Yellow pigments

What happens in light-dependent reactions?

Light energy is converted into ATP and NADPH

What is the role of light?

Excites electrons in chlorophyll

Why is ATP produced?

Provides energy for Calvin Cycle

Why is NADPH produced?

Carries high-energy electrons

What happens to oxygen?

Released as a byproduct

H₂O in light reactions

Source of electrons; splits to release O₂

Oxygen-evolving complex (OEC)

Splits water into O₂, H⁺, and electrons

P680

Primary electron donor in Photosystem II

Phaeophytin

First electron acceptor in PSII

Plastoquinone (PQ)

Carries electrons to cytochrome complex

Cytochrome complex

Pumps protons to build gradient

Plastocyanin (Pc)

Transfers electrons to Photosystem I

P700

Primary electron donor in Photosystem I

Iron-sulfur complex

First electron acceptor in PSI

Ferredoxin (Fd)

Transfers electrons to FNR

Ferredoxin-NADP⁺ reductase (FNR)

Makes NADPH from NADP⁺

NADPH

Final electron carrier (energy output)

A CAM plant tastes sour because it stores fixed carbon mainly as:

Malic acid

Plastids evolved from:

Cyanobacteria

If PSII is inhibited but PSI is functional, which pathway can still generate ATP?

Cyclic photophosphorylation

If a plant cannot regenerate RuBP efficiently, which Calvin cycle consequence is most likely?

Carbon fixation slows because RuBP becomes limiting

A mutant plant has normal chlorophyll a but lacks most accessory pigments. Under full sun it performs reasonably, but under canopy shade it performs poorly. The best explanation is that the mutant

Captures a narrower range of light wavelengths

In a lab experiment, a plant is exposed to conditions that increase O2 relative to CO2 in leaves. You observe decreased net sugar production despite continued light reactions. Which chain of events best explains the decrease?

High O₂ causes Rubisco to favor photorespiration over carbon fixation, reducing glucose synthesis despite ongoing light reactions

A mutation disrupts plasmodesmata formation. Which effect is most directly predicted?

Reduced cell-to-cell communication through shared cytoplasm

A student applies a herbicide that specifically disables the oxygen evolving complex (OEC). The plant is still able to run cyclic photophosphorylation. Which set of products will drop most immediately?

O2 and NADPH

Primary cell walls are typically:

Thin and flexible; laid down during growth