Patterns In Nature 2

Question 0

Is there movement in and out of cells?

Answer 0

Yes.

Gases, nutrients, water and mineral salts must go in; wastes and products must go out.

Question 1

What are the major groups of substances found in living cells?

Answer 1

Lignin

• noncarbohydrate substance
• organic compound
• helps the cell walls of a plant cell to bind
• strengthens it to be rigid and impermeable to water
• commonly found in tree bark

Carbohydrates

• a source of energy
• e.g. starch (stored energy in plants), cellulose (structural part of plant cell wall) and glycogen (energy stored in granules in the cytoplasm of animal cells)

Proteins

• structural components in cells and tissues
• important structural of cell membranes - regulates the passage of substances through cell membrane
• important partner wither other molecules e.g. DNA
• functional roles e.g. enzymes
• a chain of amino acids

Lipids

• fats: energy storage
• oils: energy storage
• waxes: waterproof coatings on leaves and fruits
• steroids: forms part of membranes, e.g cholesterol, coordinate functions and sex hormones

Vitamins

• there are water soluble and fat soluble vitamins
• coenzyme
• tissue formation
• pigments in eyes for vision
• maintains structure of muscle
• prevents oxidation of harmful chemicals
• blood clotting

Water

• transportation of materials
• photosynthesis
• maintenance of life
• solvent

Mineral Ions

• assist in chemical reactions by helping enzymes to function
• synthesis of many macromolecules
• sodium and chloride ions assist in water balance

Question 2

What is the current mode of membrane structure? Explain.

Answer 2

Fluid Mosaic Model, proposed by J. Singer and G. Nicholson in 1972.

Proposed a lipid sea that was filled with various proteins.

Accepted because it accounted for most functions associated with cell membranes.

• behaviour of cell membrane
• estimated surface area
• chemical analysis
• electron microscope

The lipid component is made up of a bilayer of phospholipids. The heads (phosphate) are hydrophilic and the tails (lipid) are hydrophobic.

This bilayer is not rigid, thus “fluid.” It is semi-permeable.

Protein components
- different proteins are spread out in the bilayer
Roles:
- receptor: bind substances by hormones and bring changes to the cell’s activities
- recognition: identify foreign substances, attach to carbohydrate molecules, form antigens
- adhesion: allow cells to join together
- transport: penetrate and form channels

Question 3

The permeability of a cell’s membrane depends on what?

Answer 3

• size
• electrical charge
• lipid solubility

Question 4

Describe some evidence that support the fluid mosaic model.

Answer 4

• membrane allows lipid-soluble substances to pass through
• behaviour of membrane and how it can reseal without puncture
• total area of the membrane is twice the surface area of the cell, suggesting a bilayer
• an earlier model - lipids coated by proteins - was supported with electron microscope. The current model is an improvement; to accounts for the fact that no membrane is identical.

Question 5

Compare the process of diffusion and osmosis.

Answer 5

Diffusion is the movement of any molecules from an area of high concentration to an area of low concentration - movement along a concentration gradient. It requires no energy.
e.g. simple diffusion: oxygen in he air
e.g. facilitated diffusion: where proteins in a cell membrane accelerate the movement of molecules across the membrane either by channel or carrier protein.
Carriers binds to the solute and changes shape to move it. Channels open and close according to electrical or physical signals. e.g. plant roots absorb minerals in the soil.
Water movement through cell membranes are also called facilitated diffusion because it requires protein channels- aquaporins.

Osmosis the movement of water from where it is in a high concentration, to a low concentration.

Question 6

What is active transport?

Answer 6

Where the movement of molecules from an area of low concentration to an area of high concentration require energy. e.g. glucose and amino acids being reabsorbed by kidney cells.

Question 7

Explain how the surface area to volume ratio affects the rate of movement of substances in and out of cells.

Answer 7

The volume of a cell determines its metabolic needs and waste products.

The surface area determines how fast it can absorb or excrete substances.

As the cell size increases, the surface area to volume ratio decreases, and so does the reaction rate. The smaller the volume, the more efficient the movement of substances will be.

This is why large animals are suited to cold climates and small to hot.