Origins and Benefits of Multicellularity

Question 1

How many times did multicellularity arise?

Answer 1

6 times

Question 2

what is a molecular clock?

Answer 2

Technique used to estimate the time when two or more forms diverged and is based on the mutation rate of DNA

Question 3

multicellular animals limitations in exchange

Answer 3

• SA:V ration of a multicellular organism of a multicellular organism is small
  
  • Distance of internal cells to external environment is large
  • Therefore you cannot properly expel waste or take up products from your environment through diffusion

Question 4

how do some organisms use diffusion only?

Answer 4

• Cells of many multicellular aquatic organisms are close to the external environment
  
  • Diffusion occurs directly between the cells of body and the external environment
  • Hydra and sponges have central cavities
  • These are highly branched
  • These are called gastrovascular systems

Question 5

How is an internal environment formed and what is its purpose?

Answer 5

• Cells meet their exchange needs with an internal aqueous environment (extracellular fluid)
  
  • A barrier is needed to create an internal environment
  • The internal environment is kept stable by homeostasis

Question 6

what is a circulatory system and what is its purpose?

Answer 6

• Movement of extracellular fluids around the body to ensure exchanged substances from exchange organs reach the cells of the body (bulk flow)
  
  • Ensures optimal
    ○ Gas exchange
    ○ Nutrient mobilisation
    ○ Waste removal
    ○ Intercellular communication
  • To maintain high levels of metabolism
    ○ Highly branches internal transport systems
    ○ Rapid movement of exchange substances
  • Considerable force required to move fluids through these transport systems
  • There are active and passive processes of this
    Including transpiration in plants

Question 7

what are the properties of exchange surfaces?

Answer 7

• Have a large SA- long, flat and branched
  
  • Thin surface with small diffusion distances
  • Groups of cells whose function is to exchange with the environment

Question 8

What is ficks law?

Answer 8

• Rate of diffusion= (SA x Partial pressure x Diffusion coefficient) / diffusion distance

Question 9

How to maximise diffusion

Answer 9

• Large surface areas
  
  • Maximises the partial pressure gradient
  • Minimises the diffusion that takes place in an aqueous medium
  • Thin barrier (minimises diffusion distance)

Question 10

what is homeostasis?

Answer 10

self-regulating process where biological systems remain stable whilst adjusting to changing external conditions

Question 11

what are the systems that respond to changes in order to maintain homeostasis?

Answer 11

• Receptors
  
  • Control centres
  • Effectors

Question 12

what is positive feedback?

Answer 12

• When something responds and increases the original stimulus
  
  • Blood clotting, triggering more clotting

Question 13

what is negative feedback?

Answer 13

• When the response reduces the initial stimulus
  
  • High BG reducing BG