IB BIO TOPIC 2.3/2.4 : PLANT & ANIMAL CELLS/ MEMBRANES

Question 1

What are the 3 main parts of a plant cell that animal cells lack ?

Answer 1

1. Cellulose wall 2. chloroplasts 3. Large central vacuole

Question 2

What is the composition of a plant cell wall ?

Answer 2

Cellulose microfibrils

Question 3

What are the 3 the function of a cell wall ?

Answer 3

1. Provides physical protection 2. Prevents excessive water uptake precluding bursting in hypotonic environment 3. produces turgor pressure which holds whole plant up against the force of gravity.

Question 4

What is the source of the extracellular matrix in animal cells and what are the 3 functions ?

Answer 4

The extracellular matrix is formed by a secretion of glycoproteins from the cell. 1. support 2. adhesion 3. movement

Question 5

What are the 5 main parts of a membrane ?

Answer 5

1. Phospholipid bilayer 2. Cholesterol 3. Glycoproteins 4. Integral proteins embedded in the phospholipid of the membrane. 5. Peripheral proteins attached to the phospholipid surface

Question 6

How do Hydrophobic and Hydrophilic properties of Phospholipids help maintain the structure of the membrane ?

Answer 6

1. Hydrophobic fatty acids tails repel water and form the middle layer of the membrane. 2. Hydrophilic phosphate heads attract water and form the outer layers of the membrane.

Question 7

What are the main features of the phospholipids (head) ?

Answer 7

1. Polar 2. Hydrophilic 3. They make the outside of the phospholipid layer

Question 8

What are the main features of the phospholipid tail ?

Answer 8

1. Non polar 2. Hydrophobic 3. Located inside the membrane

Question 9

Explain how phospholipids work to form a membrane ?

Answer 9

Because one end of the phospholipid is Hydrophilic and the other is Hydrophobic, they naturally form bilayers in which the heads are facing outwards and the tails are facing inward. STABLE STRUCTURE IS FORMED

Question 10

List the 6 functions of membrane proteins

Answer 10

1. Hormone binding sites 2. Immobilised enzymes 3. Cell adhesion 4. Cell to cell communication 5. Channels for passive transport 6. Pumps for active transport

Question 11

Define “diffusion”

Answer 11

The passive movement of particles from a region of higher concentration to a region of lower concentration.

Question 12

Define “osmosis”

Answer 12

The passive movement if water molecules across a partially permeable membrane, from a region of lower solute concentration to a region of higher solute concentration.

Question 13

Define “concentration gradient”

Answer 13

Molecules can diffuse across membranes from areas of higher to lower concentration by : simple or facilitated diffusion.

Question 14

What is simple diffusion ?

Answer 14

Travelling directly through the membrane if they are small and uncharged, thus avoiding repulsion by the hydrophobic, non polar tails of phospholipids in the middle of the membrane.

Question 15

What is facilitated diffusion ?

Answer 15

Travelling through special transport proteins, if they match the shape and charge requirements to fit through the channels provided by the transport proteins.

Question 16

Define the term “against concentration gradient”

Answer 16

Moves substances from an area where it is in lower concentration to an area where it is in higher concentration.

Question 17

What are the 2 main facts about protein pumps ?

Answer 17

1. Integral protein pumps embedded within membrane 2. Specific to molecule transported.

Question 18

How do protein pumps get the energy from ?

Answer 18

1. usually provided by ATP 2. Often by phosphorylating the protein pump as ATP is hydrolysed.

Question 19

What does Protein synthesis do in the transport of material in a cell ?

Answer 19

RER produces proteins which travel through the lumen (gap in tube) of the ER.

Question 20

How are vesicles used to transport materials within a cell ?

Answer 20

Membrane produced by the RER flows in the form of transport vesicles to the Golgi, carrying proteins within the vesicles to the plasma membrane where exchange such as exocytosis and endocytosis can be achieved.

Question 21

How does the modification process work ?

Answer 21

Golgi apparatus modifies proteins produced in ER

Question 22

How are proteins transported to the membrane ?

Answer 22

Golgi pinches off vesicles that contain modified proteins and travel to the plasma membrane.

Question 23

What is exocytosis ?

Answer 23

Vesicles then fuse with plasma membranes, releasing their contents outside the cell.

Question 24

How does the fluidity of the membrane allows it to change shape, break and reform during endocytosis and exocytosis ?

Answer 24

1. Lipids move laterally in a membrane, but flip flopping across a membrane is rare . 2. Unsaturated hydrocarbon tail of phospholipids have kinks that keep the molecules from packing together, enhancing membrane fluidity. 3. cholesterol reduces membrane fluidity by reducing phospholipids movement at moderate temperatures but it also hinders solidification at low temperatures.

Question 25

State similarities between prokaryotic and Eukaryotic cells

Answer 25

Both have a cell membrane Both contain ribosomes Both have DNA and cytoplasm

Question 26

State the differences between prokaryotic and Eukaryotic cells

Answer 26

Question 27

State the differences between plant and animal cells

Answer 27

Question 28

Outline two roles of extracellular components.

Answer 28

The plant cell wall maintains cell shape, prevents excessive water uptake, and holds the whole plant up against the force of gravity.

Animal cells secrete glycoproteins that form the extracellular matrix. This functions in support, adhesion and movement.