Cell theory

Question 1

Distinguish between diffusion and osmosis

Answer 1

• Diffusion is the net movement of molecules in an area of high concentration to an area of low concentration.
• Osmosis is the diffusion of water across a partially permeable membrane, water molecules move from an area of low concentration to an area of high concentration.

Question 2

Explain how the properties of phospholipids help to maintain the structure of the cell surface membrane

Answer 2

Hydrophilic head groups point outward and the hydrophobic tails form a lipid bilayer. Ions and polar molecules are not able to cross the membrane. That helps the cell maintain internal concentration and exclude other molecules.

Question 3

State the composition and the function of the plant cell wall

Answer 3

It is made up of cellulose. Cellulose molecules are arranged in bundles called microfibrils. These give the cell wall great tensile strength and allow high pressures to develop inside the cell.The cellulose cell wall consists of three layers: middle lamella, primary cell wall, and secondary cell wall. The overall functions the cell wall preforms are: structure, support, protection.

Question 4

Define the term diploid

Answer 4

a cell or an organism with two sets of chromosomes.

Question 5

State three activities that occur during part A of the cell cycle

Answer 5

• Protein synthesis
• DNA replication
• Cell growth

Question 6

Outline the differences in cytokinesis in animal and plant cells

Answer 6

Animal cell:

• occurs through cleavage
• a cell plate is not formed
• a mid body develops centrally
• spindle degenerates during cytokinesis

Plant cell:

• cleavage cytokinesis occurs only in lower plants. higher plant cells show cell plate cytokinesis.
• vesicles fuse to form cell plate
• cell wall is built

Question 7

Explain the significance of complementary base pairing in relation to the cell cycle

Answer 7

The ‘‘A’’ part of the cell cycle (interphase), involves DNA synthesis. Replication of DNA requires complementary base pairing, A-T and C-G. It produces two identical copies of DNA / sister chromatids. The sister chromatids split in anaphase. Each new cell gets a copy of each DNA molecule. Genetically wrong base pairing causes mutations. Mutations can lead to cancer.

Question 8

List the functions of membrane proteins

Answer 8

hormone binding sites
electron carriers
pumps for active transport
channels for passive transport
enzymes
cell to cell communication
adhesion

Question 9

Lysosome

Answer 9

hydrolysis

Question 10

Golgi apparatus

Answer 10

synthesis

Question 11

Rough ER

Answer 11

site of synthesis of proteins

Question 12

Nucleus

Answer 12

controls cell activities

Question 13

Mitochondria

Answer 13

generates ATP

Question 14

Describe the process of active transport

Answer 14

uses/ requires energy/ ATP
goes against concentration gradient/ lower to higher concentration
requires a protein in the cell membrane/ pump/ carrier protein (reject channel)
hydrolysis of ATP/ ATP –> ADP + phosphate
involves a conformational change in the pump/ protein/ diagram to show this

Question 15

Outline the process of endocytosis

Answer 15

• Formation of vesicles
• Infolding of cell membrane
• Organisms are engulfed
• Phagocytosis is called feeding in some unicellular organisms
• Called pinocytosis when the solutions are taken in
• Vesicles are much smaller
• May be receptor mediated
• Requires energy

Question 16

Distinguish between plant cells and animal cells

Answer 16

Plant cells:

• have cell walls, animal cells do not
• have chloroplasts, animal cells do not
• have a large central vacuole, animal cells do not
• store starch, animal cells store glycogen
• have plasmodesomata, animal cells do not

Animal cells:

• have centrioles, plant cells do not
• have cholesterol in the cell membrane, plant cells do not
• plant cells generally have fixed shape, whereas animal cells are more rounded