Gas Exchange, Cell Membranes & Transport (Edexcel International A Level (IAL) Biology): Flashcards

True.

The alveolar wall consists of a single layer of flattened (squamous) epithelial cells to allow efficient diffusion of gases.

Oxygen diffuses from the alveoli into the capillaries to be carried around the body.

The cell surface membrane is the membrane that surrounds the cell, creating an enclosed space that separates the internal environment from the external environment.

Intracellular membranes form compartments within the cell, such as the nucleus, mitochondria, and endoplasmic reticulum.

Membranes control the exchange of substances and act as an interface for communication.

False.

Membranes are partially permeable, allowing some substances to cross while blocking others.

Phospholipids contain a polar head and two non-polar tails.

Phospholipids contain a polar head and two non-polar tails.

The fluid mosaic model describes the structure of cell membranes as a mosaic of proteins and phospholipids that can move fluidly within the bilayer.

Cholesterol regulates membrane fluidity by preventing the membrane from becoming too rigid at low temperatures and too fluid at high temperatures.

A model in science is a representation of real world ideas, organisms, processes, or systems that cannot be easily investigated directly.

False.

Models can change on the basis of new discoveries. If new features are found that do not fit the current model, the model is altered or replaced.

The fluid mosaic model of cell membrane structure was first proposed in 1972 by Singer and Nicolson.

The fluid mosaic model describes membranes as fluid, with globular proteins both peripherally and integrally embedded in a phospholipid bilayer, allowing movement and flexibility crucial for membrane function.

Membrane permeability is the ability of the cell membrane to allow substances to pass through it.

Beetroot cells contain a dark purple-red pigment, which leaks out when the membrane is more permeable.

A colorimeter is used to measure the amount of pigment released from beetroot cells.

True.

Greater membrane permeability allows more pigment to escape from the beetroot cells into the surrounding solution.

A colorimeter measures how much light is absorbed as it passes through a coloured liquid sample.

Calibrating the colorimeter means zeroing the colorimeter using distilled water in a cuvette before taking measurements.

Cuvettes are small cuboid containers used to hold samples in a colorimeter.

As temperature increases, membrane permeability increases because phospholipids move more and are less tightly packed, and proteins may denature.

Using beetroot pieces of equal size ensures that all samples have the same surface area and volume, so the rate of pigment leakage is not affected by size differences.

As alcohol concentration increases, membrane permeability increases.

Denaturation of membrane proteins is the loss of their 3D structure due to high temperature, making the membrane more permeable.

True.

Scratched or thicker cuvettes absorb more light, potentially skewing the results of the experiment.

Ice crystals can pierce the cell membrane at very low temperatures, increasing permeability.

Osmosis is the net movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane.

A partially permeable membrane allows small molecules like water to pass through, but not larger molecules such as solutes.

Osmosis is the net movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane.

Water potential is a measure of the tendency of water molecules to move. Pure water = 0 kPa and solutions have negative water potential.

A water molecule is free if it is not surrounding dissolved substances. When water surrounds a dissolved substance, it is no longer free and cannot move through a membrane readily.

When a substance dissolves in water, the water molecules that surround it are no longer free and cannot move through a membrane as easily.

True.

Osmosis is a specialised form of diffusion because water moves down its concentration gradient through a partially permeable membrane.

Water molecules can pass through the bilayer because of their small size, even though they are polar.

The cytoplasm is the part of the cell that consists of water and dissolved substances, giving it its own water potential.

Animal cells take in water by osmosis and may burst because they do not have a cell wall to prevent swelling.

When a plant cell is placed in pure water, it swells as water moves in by osmosis, but the cell wall prevents it from bursting.

Water moves out of the cells by osmosis. Animal cells shrivel, while in plant cells, the vacuole and cytoplasm shrink but the cell wall maintains the cell's shape.

Active transport is the movement of molecules and ions through a cell membrane from a region of lower concentration to a region of higher concentration, requiring energy from ATP to move substances against their concentration gradient.

Active transport requires energy in the form of ATP, and uses carrier proteins.

ATP provides the energy required for carrier proteins to change shape, enabling the movement of molecules or ions across the membrane against their concentration gradient.

False.

Active transport moves substances against their concentration gradient.

Diffusion is the net movement of a substance from a region of its higher concentration to a region of its lower concentration, down a concentration gradient.

Diffusion is a passive process and does not require energy.

Small and non-polar molecules, such as oxygen and carbon dioxide, can move across membranes by simple diffusion.

Facilitated diffusion is the passive movement of molecules or ions across a membrane via specific transport proteins.

False.

Facilitated diffusion is a passive process and does not require ATP; it moves molecules down their concentration gradient via proteins.

Endocytosis is the process by which a cell engulfs large molecules or particles by surrounding them with its membrane to form a temporary vacuole.

False.

Exocytosis is an active process that requires energy to move substances out of the cell.

During exocytosis, vesicles containing substances fuse with the cell surface membrane to release the contents outside the cell.