BIOL 371 Multicellularity in Archaeplastida

What is the order of events of plant and animal divergence?

1. origin of life

2. origin of eukaryotes

3. great oxygenation event

4. mitochondriate eukaryotes

5. last common ancestor, origin of plastids

6. increasing occurrences of multicellularity

Why do plastids within the eukaryotic cell reduce the requirement for phagocytosis for nutrient acquisition?

Plastids reduce the requirement for phagocytosis by enabling photoautotrophy, which allows cells to synthesize their own biomolecules directly from CO2, water, and sunlight. Once a eukaryote acquires a plastid, it no longer needs to actively hunt, engulf, and digest particulate matter to satisfy its carbon and energy requirements.

Why do plastids within the eukaryotic cell increase the need for cellular water?

Plastids increase a cell's need for water because they are osmotically active and directly consume water as a reactant in photosynthesis.

Secondary endosymbiosis

the subsequent uptake of a red and/or green alga by other non photosynthetic eukaryotes giving rise to several aquatic algal lineages and phytoplankton

Photosynthesis summary

• Light energy is used in the thylakoid membranes to split water (H₂O) into O₂, H⁺ ions, and electrons.

• The H⁺ ions build up inside the thylakoid, then flow through ATP synthase into the stroma, producing ATP (chemiosmosis).

• The electrons travel through an electron transport chain, reducing NADP⁺ to NADPH (using H⁺ from the stroma).

• ATP and NADPH provide the energy and reducing power for the Calvin cycle in the stroma.

• The Calvin cycle begins with the enzyme Rubisco, which fixes CO₂, eventually producing carbohydrates (polysaccharides such as glucose/starch).

Are all plants photosynthetic?

no, but all have photosynthetic ancestry

Why have some plants lost the ability to photosynthesize?

In favor of alternative nutrient acquisition strategies

mycoheterotrophs

obtain carbon source from fungal associations with other plants

Parasitic plants

obtain carbon source directly from other plants

Do plants have plasma membrane junctions?

no

Why are cell walls able to form in plants?

because of their reduced requirement of phagocytosis since they make their own food

What are primary cell walls main function?

They provide support and protection but allow for flexibility

What is the main purpose of the vacuole?

gives rigidity to the cell using turgor pressure dictated by the surrounding environments

Where is the primary cell wall?

outside the plasma membrane

Why are plants crucial to diet?

They contain cellulose which itself is hard to digest making it a major component of dietary fibre or roughage helping move food through preventing constipation

Because humans lack the necessary enzyme to break its bonds, it passes through the gastrointestinal tract intact, adding bulk and promoting peristalsis to move food efficiently and prevent constipation.

What are some characteristics of the cell wall?

porous, allowing nutrients and water to pass through

provides tensile strength preventing cell from bursting under hypotonic conditions or collapsing under hypertonic conditions

How do plant cells regulate water?

acquire/lose through osmosis

How does the cell create turgor pressure?

Water follows solutes.

High solute concentration in the vacuole pulls water into the cell vacuole, helping the plant stay rigid instead of wilting by pushing the plasma membrane outward and against the cell wall

What is the turgid state?

the ideal state for plant cells that help maintain the structure of the plant and maintain osmotic balance

What happens when mechanosensors activate ion channels?

Ions move across the membrane, changing the cell's osmotic potential and causing water to move.

Can plants generate action potentials? What is the purpose of plant action potentials?

Yes. Plants can produce electrical signals (action potentials) similar to those in animal cells. They coordinate responses between nearby cells, tissues, or organs. Cells losing turgor generates and action potential allowing them t move.

What do end products of multicellularity from algal linneages tell us?

processes are unique and can be used to distinguish evolutionary trends

*Because of this, we know that all land plants are descended from the same clade of eukaryotic green algae

How does multicellularity cause specialization?

True multicellularity involves the specialization of cells to perform different functions

Allows for coordinated behaviour of different tissues to aid in the fitness of the organism as a whole

Are land plants unicellular or multicellular?

all land plants and multicellular

What is a phragmoplast?

an arrangement of the microtubules allowing for cell wall deposition between the the two separated nuclei prior to the complete division of the cytoplasm

What does the deposition of the cell wall require?

• arrangement of phragmoplast microtubules

• fusion of vesicles from ER and golgi

How are plasmodesmata created?

portions of ER trapped within the newly created cell wall creates connections between two daughter cells known as plasmodesmata

What are plasmodesmata?

intercellular connections between plant cells allowing for cell to cell transport of cytoplasmic contents

When do plasmodesmata form? What about secondary plasmodesmata?

during cell division, secondary can develop in some cells through degradation of the cell wall

What is analogous to gap junctions in plant cell walls?

plasmodesmata

What is the desmotubule?

the ER within the cell wall cavity that regulates the passage of materials through the plasmodesmata

What are the defining characteristics of plants?

• sessile

• have phototrophic ancestry

• primary cell walls composed of cellulose and hemicellulose

• multicellular