exchange and transport

What model describes the structure of the plasma cell membrane?

The fluid mosaic model, proposed by Singer and Nicholson in 1972.

Why is the plasma membrane described as 'fluid'?

It has liquid-like properties, allowing movement of components within it.

What does 'mosaic' refer to in the fluid mosaic model?

The diverse components, including proteins and lipids, that make up the membrane.

What is the main component of the plasma membrane?

Phospholipids, which make up about 75% of the membrane.

How are phospholipids arranged in the cell membrane?

They form a bilayer with hydrophilic phosphate heads pointing outward and hydrophobic tails inward.

What role does cholesterol play in the plasma membrane?

Cholesterol, making up about 20% of the membrane, provides stability.

What types of proteins are found in the plasma membrane?

Some proteins are part of the inner layer, some are enzymes, and others span across the bilayer as carriers and channels.

What are glycoproteins and glycolipids, and what is their function?

They are molecules on the outer layer of the membrane that facilitate cell communication and signaling.

How do receptor proteins function in cell signaling?

They have specific shapes that allow only complementary messenger molecules to bind to them.

What factors can be investigated to study the permeability of the cell membrane?

Temperature, solvent type (e.g., ethanol, methanol), and solvent concentration.

What is diffusion?

The movement of substances from an area of higher concentration to an area of lower concentration.

What types of molecules can pass through the phospholipid bilayer via simple diffusion?

Gases (e.g., O2, CO2), hydrophobic molecules (e.g., benzene), and small polar molecules (e.g., water, ethanol).

What is Fick's Law?

It describes the relationship between factors affecting the rate of gas diffusion across a membrane.

How do small charged molecules like sodium ions enter cells?

Through protein channels via facilitated diffusion.

What is the role of carrier proteins in the cell membrane?

They facilitate the movement of larger polar molecules, like glucose, through conformational changes.

What are aquaporins?

Channels that allow water to travel by facilitated diffusion.

What is osmosis?

The movement of water molecules from a region of high water potential to low water potential across a partially permeable membrane.

What happens to water molecules that are attracted to solute molecules during osmosis?

They become 'bound' and are no longer free to diffuse through the membrane.

What are two roles of glycoproteins in the cell membrane?

Facilitating cell communication and serving as receptors for signaling molecules.

What happens to cell membrane structure at temperatures below 0°C?

The membrane may become rigid and less permeable, affecting cell function.

How have cell membranes adapted for animals living in colder climates?

They may contain more unsaturated fatty acids to maintain fluidity at lower temperatures.

What is water potential and how is it measured?

Water potential is a measure of the potential energy of water in a system, measured in kiloPascals (kPa). Pure water has a water potential of 0 kPa.

How does adding solutes affect water potential?

Adding solutes lowers water potential, resulting in negative values for solutions.

What is turgor pressure in plant cells?

Turgor pressure is the hydrostatic pressure inside plant cells that results from water absorption, causing the cell to swell and become firm (turgid).

What happens to plant cells in a high water potential environment?

Plant cells absorb water by osmosis, increasing hydrostatic pressure and causing the cell to swell.

What is plasmolysis?

Plasmolysis occurs when a plant cell loses water in a solution with lower water potential, leading to a decrease in hydrostatic pressure and the membrane detaching from the cell wall.

What occurs in animal cells when water potential is too low?

Water leaves the cells by osmosis, hydrostatic pressure decreases, and cells become crenated.

What is haemolysis in red blood cells?

Haemolysis is the bursting of red blood cells due to increased hydrostatic pressure when water enters the cells by osmosis.

What are triglycerides and their role in energy storage?

Triglycerides are insoluble energy storage molecules in animals and plants that bundle together to form insoluble droplets and have hydrophobic fatty acid tails.

What is phagocytosis?

Phagocytosis is a type of bulk transport where cells, such as phagocytes, engulf large particles or organisms.

Describe the stages of phagocytosis.

1. Food material is surrounded by pseudopodia. 2. It forms a phagocytic vacuole (phagosome). 3. Lysosomes fuse with the phagosome and release enzymes to digest the material. 4. Undigested material remains in the vacuole, which moves towards the cell membrane for egestion.

What is pinocytosis?

Pinocytosis is a form of endocytosis that allows cells to take in small particles suspended in extracellular fluid.

What are the two main purposes of exocytosis?

Exocytosis serves to eject undigested particles and secrete extracellular substances such as hormones and enzymes.

What is the role of membrane proteins in facilitated diffusion?

Membrane proteins facilitate the transport of specific molecules across the cell membrane without the use of energy.

What is the difference between endocytosis and exocytosis?

Endocytosis is the process of taking substances into the cell, while exocytosis is the process of expelling substances from the cell.

What type of lipid mainly composes cell membranes?

Cell membranes mainly consist of phospholipids.

What molecule in cell membranes restricts the movement of other molecules?

Cholesterol molecules restrict movement and maintain membrane structure.

Name five ways that molecules can move across a cell membrane.

1. Simple diffusion 2. Facilitated diffusion 3. Active transport 4. Endocytosis 5. Exocytosis.

What adaptations can increase the rate of movement of ions and water-soluble molecules across membranes?

Increasing the surface area of the cell membrane is one adaptation that can enhance movement rates.

What properties allow a molecule to cross the phospholipid bilayer by facilitated diffusion?

Molecules that are small, polar, or have specific transport proteins can cross the phospholipid bilayer by facilitated diffusion.

How do the structures of lipids and carbohydrates suit them for energy storage?

Lipids are hydrophobic and form compact energy storage molecules, while carbohydrates provide quick energy release.