Download H/Ws 1 to 4

H/Ws 1 to 4.
Types
Cells
Structure
Response
Q: Why are cells important?
A: Basic unit of Life: reproduce, metabolize, respond to stimuli,
grow, and die.
Q: what are the two main types of cells?
A: Prokaryote and Eukaryote.
Prokaryote
DNA material
DNA in nucleoid
No organelles
Have cytoplasm
0.1 – 10micrometers in size
All reactions in one
compartment
Eukaryote
DNA material
DNA in nucleus
Have organelles
Have cytoplasm
10 – 100micrometers in size
Different reactions in
different compartments
Q: Why is Surface Area to Volume ratio important?
A: Need to have fast exchange of materials between cell and
external environment. Therefore need high surface area to
volume ratio. That is why as an organism increases in size it
increases the number of cells NOT size of the individual cells Fig.
6.7.
Q: What are the two types of Eukaryote cells?
A: Plant and animal cells.
Plant Cell
Nucleus and other organelles
Cytoskeleton
Plasma membrane
Chloroplast
Cell wall
Central vacuole
Tonoplast
Plasmodesmata
Animal Cell
Nucleus and other organelles
Cytoskeleton
Plasma membrane
N/A
N/A
N/A
N/A
N/A
Lysosomes
Flagellum
Fig. 6.9.
Q: What are lysosomes and their function?
A: Sac of hydrolytic enzymes (hydrolysis).
-Carry out intracellular digestion.
-Recycle the cell’s own organic material ( autophagy).
-Fig. 6.14 phagocytosis and autophagy (breakdown of
damaged organelles).
Q: What are vacuoles?
A: Similar to lysosomes but have other functions:
- Food vacuole =formed by phagocytosis.
- Contractile vacuole = pumps out excess water Ex. in fresh water
protists.
- Central vacuole (plants) = holds food reserves (proteins,
inorganic ions).
- Disposal of metabolic byproducts.
- Contain pigments.
- Protect against predators (poisons).
- Gets larger as cell grow so little cytoplasm. Cytosol
therefore a small proportion of cell and ratio of membrane
surface area to cytosolic volume is great, even for a large plant.
Q: What is the fluid mosaic model?
A: A membrane and various proteins embedded or attached to the
double phospholipids layer.
Q: Why a bilayer?
A: This arrangement allows for a stable boundary between two
aqueous compartments (water inside and outside of the cell).
Q: Where do the proteins fit in the membrane?
A: The difference in adherence of the cell membrane (CM), to
water is due to the hydrophilic proteins in the membrane. Only
the hydrophilic region exposed to water. Hydrophobic region in
the membrane.
Q: Why is it important to maintain the fluidity of the CM?
A: Needs to be permeable and activity of enzymes in membrane
affected.
Q: How is the CM kept from solidifying?
A: Cholesterol is the “temperature buffer.” As temperature goes
down close packing of phospholipids prevented by the cholesterol
and so lowers the temperature required for solidification.
The type of lipid determines the fluidity of the membrane.
Saturated pack closer together than unsaturated lipids.
Usually membranes are as fluid as salad oil.
Fig. 7.5. Hydrophobic interactions which are weaker than
covalent.
Fig. 7.7 and 7.9. Structure and functions.
Q: What is a key function of any biological membrane?
A: A key function of a biological membrane is regulation of
transport of molecules into and out of the cell.
Example of form fitting function.
Q: How is a membrane selectively permeable?
A:
- Non-polar molecules ( hydrocarbons, O2, CO2), dissolve in
the lipid bilayer and cross.
- Ions and polar molecules (glucose, water, Na+ etc), need
transport proteins.
a) Channel proteins that have a hydrophilic channel (like a
tunnel). Water goes through aquaporins (nobel prize 2003 –
Dr. Agre).
b) Carrier proteins actually hold molecule and change shape so
that molecule is moved across membrane.
- Concentration gradient. Molecules diffuse down a
concentration gradient form high to low. Requires no energy
even if facilitated by membrane proteins.
- Active transport is against the concentration gradient and
requires energy (ATP).
Review Questions:
1. Why is a high surface area to volume ration so important to a cell?
2. What are the two main types of cells? What are the differences and similarities?
3. How does the central vacuole help a plant keep a high SA: Vol ratio as it grows?
4. Draw a phospholipids bilayer and explain how form fits function.
5. What determines the fluidity of a bilayer membrane?
6. What is the role of cholesterol in membrane structure?
7. Go over fig. 7.7 and be able to identify and describe functions of all the components.
Review Questions:
1. Why is a high surface area to volume ration so important to a cell?
2. What are the two main types of cells? What are the differences and similarities?
3. How does the central vacuole help a plant keep a high SA: Vol ratio as it grows?
4. Draw a phospholipids bilayer and explain how form fits function.
5. What determines the fluidity of a bilayer membrane?
6. What is the role of cholesterol in membrane structure?
7. Go over fig. 7.7 and be able to identify and describe functions of all the components.