Movement into and out of cells

Question 1

What is Diffusion?

Answer 1

Diffusion is the movement of molecules from a region of its higher concentration to a region of its lower concentration
Molecules move down a concentration gradient, as a result of their random movement

Question 2

Diffusion Across the Cell Membrane: Principle of Movement

Answer 2

Same as non-living cells – movement down a concentration gradient.
Cell surrounded by a partially permeable membrane.

Question 3

Diffusion Across the Cell Membrane: Cell Membrane

Answer 3

Nature: Partially permeable.
Function: Allows some molecules to cross easily, while others with difficulty or not at all.

Question 4

Diffusion Across the Cell Membrane: Purpose of Diffusion

Answer 4

Benefits:
Obtain many requirements.
Get rid of waste products.
Carry out gas exchange for respiration.

Question 5

Diffusion Across the Cell Membrane: Examples in Living Organisms

Answer 5

Plants:
Require oxygen for respiration continuously.
Need carbon dioxide for photosynthesis when conditions are suitable (e.g., adequate light and temperature).

Question 6

Examples of Diffusion: Small intestine

Answer 6

Molecules Moving: Digested food products (glucose, amino acids, fatty acids, glycerol, etc.).
From: Lumen of the small intestine.
To: Blood/lymph in villi covering small intestine walls.

Question 7

Examples of Diffusion: Leaf giving off

Answer 7

Molecules Moving: Oxygen.
From: Air spaces between mesophyll cells.
To: Mitochondria in all cells.

Question 8

Examples of Diffusion: Leaf taking in

Answer 8

Molecules Moving: Carbon dioxide.
From: Air spaces between mesophyll cells.
To: Chloroplasts in mesophyll cells.

Question 9

Examples of Diffusion: Leaf with water

Answer 9

Molecules Moving: Water vapor.
From: Stomatal pores.
To: Air outside stomata.

Question 10

Examples of Diffusion: Lungs taking in

Answer 10

Molecules Moving: Oxygen.
From: Alveolar air space.
To: Blood in capillaries around alveoli.

Question 11

Examples of Diffusion: Lungs giving off

Answer 11

Molecules Moving: Carbon dioxide.
From: Blood in capillaries around alveoli.
To: Alveolar air space.

Question 12

Energy for Diffusion: Source of Energy

Answer 12

Energy for diffusion comes from the kinetic energy.
Kinetic energy originates from the random movement of molecules and ions.

Question 13

Energy for Diffusion: Particle Movement:

Answer 13

All particles move randomly continually.
This random movement is termed Brownian motion

Question 14

Factors Influencing Diffusion: Surface Area to Volume Ratio

Answer 14

Effect on Rate: Larger structures have a smaller surface area to volume ratio, slowing down substance movement.
Adaptations: Cells adapted for diffusion increase surface area, e.g., root hair cells in plants and ileum lining cells in animals.
Example: The highly folded surface of the small intestine increases its surface area.

Question 15

Factors Influencing Diffusion: Distance

Answer 15

Influence on Transport: Smaller distances lead to faster transport.
Relevance: Blood capillaries and alveoli have thin walls (one cell thick) for rapid diffusion.

Question 16

Factors Influencing Diffusion: Temperature

Answer 16

Impact: Higher temperature equals faster molecule movement due to increased energy.
Result: More collisions against cell membranes, enhancing the rate of substance movement.

Question 17

Factors Influencing Diffusion: Concentration gradient

Answer 17

Relation to Movement: Greater concentration difference results in faster movement.
Explanation: Higher concentration causes more collisions, expediting movement across the membrane.

Question 18

Water as a Solvent: Importance of Water

Answer 18

Water is crucial for all living organisms as it serves as a solvent.
Its role as a solvent is vital for life on Earth.

Question 19

Water as a Solvent: Transport Within Organisms

Answer 19

Example: Xylem and phloem in plants.
Function: Dissolved substances are easily transported, facilitating essential processes.

Question 20

Water as a Solvent: Distribution of Digested Food

Answer 20

Scenario: Digested food molecules in the alimentary canal.
Significance: Water as a solvent enables the movement of nutrients to cells throughout the body.

Question 21

Water as a Solvent: Removal of Toxic and Excess Substances

Answer 21

Examples: Urea and excess salts.
Process: Water dissolves these substances, aiding in their removal from the body through urine.

Question 22

Water as a Solvent: Role in the Cytoplasm

Answer 22

Importance: Water is a key component of the cytoplasm.
Function: Facilitates metabolic reactions within cells.

Question 23

Osmosis: Cell membrane permeability

Answer 23

All cells are enclosed by a partially permeable cell membrane.
The membrane allows selective passage of substances.

Question 24

Osmosis: Osmosis Definition

Answer 24

Process: Osmosis is the diffusion of water molecules.
Direction: Moves from a dilute solution (high water concentration) to a more concentrated solution (low water concentration).
Medium: Occurs across a partially permeable membrane.

Question 25

Osmosis: Concentration Gradient

Answer 25

Movement Direction: Water moves down its concentration gradient.
Explanation: From an area with a higher water concentration to an area with a lower water concentration.

Question 26

Osmosis: Partially Permeable Membrane

Answer 26

Characteristic: Cell membrane is partially permeable.
Permeability: Allows small molecules (e.g., water) through but restricts larger molecules (e.g., solute molecules).

Question 27

Osmosis Experiments: Immersing Plant Cells

Answer 27

Common Method: Use root vegetables like potato or radish.
Solutions: Place the cylinders in distilled water and sucrose solutions of varying concentrations.
Procedure:
Weigh the cylinders before immersion.
Leave in solutions for 20-30 minutes.
Remove, dry, and reweigh.

Question 28

Osmosis Experiments: Observations - Plant Tissue Mass:

Answer 28

Gain in Mass:
Indicates water movement into the plant tissue by osmosis.
Surrounding solution is more dilute than the plant tissue.
Loss in Mass:
Indicates water movement out of the plant tissue.
Surrounding solution is more concentrated than the plant tissue.
No Change in Mass:
Implies no net movement of water.
Concentrations in the plant tissue and surrounding solution are equal.

Question 29

Osmosis Experiments: Dialysis Tubing Experiment:

Answer 29

Membrane Characteristics: Non-living, partially permeable cellulose membrane.
Pores: Small enough to prevent large molecules (e.g., sucrose) but allow smaller ones (e.g., glucose and water).
Demonstration:
Fill tubing with concentrated sucrose solution.
Suspend in a boiling tube of water for a set period.
Observe changes in water level outside the tubing.

Question 30

Osmosis Experiments: Osmosis in Dialysis Tubing

Answer 30

Principle: Water moves from higher water potential (dilute solution) to lower water potential (concentrated solution) through a partially permeable membrane.
Explanation: Demonstrates osmosis and diffusion across the membrane.

Question 31

Osmosis in Plant Tissues: Water Entry in Plant Cells

Answer 31

When water enters a plant cell, the vacuole expands, pushing the cell membrane against the cell wall.
Water intake through osmosis contributes to cell rigidity, making it firm.
Cellular rigidity is vital for plant support, strength, and upright growth, enabling efficient sunlight exposure.
Cell wall pressure prevents excessive water entry, averting cell bursting.

Question 32

Osmosis in Plant Tissues: Wilting Due to Water Shortage

Answer 32

Insufficient water leads to the loss of cellular rigidity (turgidity), resulting in wilting.

Question 33

Osmosis in Plant Tissues: Osmosis Key Concepts

Answer 33

Definition: Net movement of water from higher water potential (dilute solution) to lower water potential (concentrated solution) through a partially permeable membrane.
Clarification: Dilute solution signifies high water potential; concentrated solution denotes low water potential.

Question 34

Osmosis in Plant Tissues: Plant Cells in Varying Solutions

Answer 34

In a dilute solution (higher water potential), water moves into plant cells via osmosis, increasing turgor pressure and making cells turgid.
In a concentrated solution (lower water potential), water exits plant cells, causing flaccidity and potential plasmolysis.

Question 35

Osmosis in Plant Tissues: Animal Cells and Osmosis

Answer 35

Animal cells undergo water loss and gain through osmosis.
Absence of a supporting cell wall in animal cells intensifies the impact of osmotic changes.

Question 36

Active Transport: Definition of Active Transport

Answer 36

Active transport is the process of moving particles through a cell membrane from a region of lower concentration to a region of higher concentration, utilizing energy derived from respiration.

Question 37

Active Transport: Importance of Active Transport

Answer 37

Energy Requirement: Active transport demands energy as particles move against their concentration gradient (opposite to diffusion).
Vital Processes: Essential for transporting molecules or ions across membranes, such as:
Uptake of glucose by epithelial cells in the villi of the small intestine.
Uptake of ions from soil water by root hair cells in plants.

Question 38

Active Transport: Protein Carriers in Active Transport

Answer 38

Active transport employs carrier proteins embedded in the cell membrane for specific molecule transport.
Process:
Substance binds with the carrier protein in the cell membrane.
Carrier protein utilizes energy from respiration, inducing a change in shape to move the substance against the concentration gradient.
The substance is released into the cell.