L17- plants and microbes

Question 1

why do all cells have the potential to be excitable?

Answer 1

All cells maintain a voltage across their membrane

Question 2

Why do plants need rapid movement?

Answer 2

• protection from damage
• catch prey
• spread pollen and seeds

Question 3

Describe the response in Mimosa pudica?

Answer 3

It’s also called the sensitive plant.
It has a rapid response to touch, light and temperature. The leaflets fold up when touched or at night. Looks as if it’s wilting.

Question 4

Why does the mimosa pudica have this response?

Answer 4

Exposes thorny stems to deter herbivores and pests. Stops dehydration at night

Question 5

What resposne does the dionea muscipula have?

Answer 5

Venus flytrap. Sensitive hairs inside, trap shuts to capture prey.

Question 6

What kind of organism is a paramecium?

Answer 6

Cilliate protozoan. (protist) single-celled organism

Question 7

What response does a paramecium have to environment?

Answer 7

It’s covered in cillia to swim. Rapidly changes direction when it bumps into something.

Question 8

How do paramecia react to a stimulus?

Answer 8

The stimulus causes change in the membrane. Receptor potential-> if exceeds threshold (ca channels open)-> ca based action potential. More ca enters. if AP big enough, the cilia will change direction

Question 9

What do paramecia behavioural mutants show us?

Answer 9

They have impaired responses to stimuli. shows which genes affect behaviour.

Question 10

Describe the AP for paramecia?

Answer 10

The voltage gated calcium channels open. Then V-gated K channels open.
The increase in intracellular CA then deactivates the Ca channels. Negative feedback. AP goes back down.

Question 11

What’s the resting potential for paramecia?

Answer 11

-40mV

Question 12

How do cilia move and how does this change direction?

Answer 12

9+2 arrangment of microtubules to create axoneme.
Protein crosslinks of dynein walk along the microtubule cause whip-like movement
Increased Ca2+ inide cell causes reversal of ciliary beat.

Question 13

Give 3 examples of behavioural mutants in paramecium?

Answer 13

1. pawn- no v gated ca channel. cant generate Ap so can;t change direction.
2. Dancer- enhanced Ca current, changes direction a lot from weak stimulus
3. pantaphobiac- reduced V gated K current- prolonged depolarisation. so swims backwards longer

Question 14

What do Didinium nasutum do?

Answer 14

Predate paramecium. Also a ciliate protozoan. Attaches with a poisonous dart, paralyses it and engulfs paramecium.

Question 15

How do mimosa pudica leaflets move?

Answer 15

The stimulus causes chloride ions to open. Chloride ions leave the vacuole passively because the inside is negative.
The K+ channels open and K follows Cl-. Then water follows by osmosis. The cells shrink, on the bottom of the pulvinus, so the pulvinus bends down.

Question 16

Why does the pulvinus always bend down?

Answer 16

The cells on the upper pulvinus have thick cell walls so dont shrink. The lower cells have thinner cell walls so can shrink, bending the pulvinus.

Question 17

Whats different about how the cells in mimosa pudica change the potential of the cell?

Answer 17

Usually Na or Ca enter the cell, making it more positive. In this case it’s chloride ions that leave the cell, making it less negative–> hence more positive.

Question 18

Whats the resting membrane potential of cells in the dionea muscipula?

Answer 18

-150mV

Question 19

What is the length of APs in the dionea musipula?

Answer 19

1-3 secs

Question 20

What are the APs of Dionea muscipula based on? (mechanism)

Answer 20

Ca2+based voltage gated calcium channels

Question 21

In the dionea muscipula, how does the AP spread from cell to cell?

Answer 21

Via plesmodesmata. (plant version of gap junctions)