Chapter 2: Cells

Question 1

Function of Cell Membrane

Answer 1

Acts as a selective barrier, controlling what enters and leaves the cell.
Made up of a phospholipid bilayer with embedded proteins.

Question 2

Passive Transport and its types

Answer 2

Movement of substances across the cell membrane without requiring energy input from the cell.
Diffusion and Osmosis.

Question 3

Diffusion with an example

Answer 3

Movement of molecules from an area of high concentration to an area of low concentration until equilibrium is reached. [e.g., oxygen moving into the cell, carbon dioxide moving out.]

Question 4

Osmosis with an example

Answer 4

Diffusion of water molecules across a semi-permeable membrane (like the cell membrane) from an area of low solute concentration (high water concentration) to an area of high solute concentration (low water concentration).
Examples: Plant cells in a hypotonic solution (weaker solution outside) will swell due to water influx.
Animal cells in a hypertonic solution (stronger solution outside) will shrink due to water efflux.

Question 5

Types of Solutions

Answer 5

Hypotonic, Isotonic and Hypertonic Solutions

Question 6

Hypotonic Solution with an example

Answer 6

A solution with a lower concentration of solutes compared to the inside of a cell.
Example: Freshwater environments for many aquatic organisms are hypotonic. Water tends to move into the cells due to osmosis, which can cause them to swell and potentially burst if not regulated.

Question 7

Isotonic Solution with an example

Answer 7

A solution where the concentration of solutes (dissolved particles) inside a cell is equal to the concentration of solutes outside the cell.
Example: Many physiological fluids in the body, like blood plasma or saline solution used intravenously, are close to isotonic. This prevents excessive water movement into or out of cells and maintains their proper function.

Question 8

Hypertonic Solution with an example

Answer 8

A solution with a higher concentration of solutes compared to the inside of a cell.
Example: Saltwater environments for marine organisms are hypertonic. Water tends to move out of the cells due to osmosis, which can cause them to shrink and shrivel if not regulated.

Question 9

Active Transport with examples

Answer 9

The movement of substances across the cell membrane against the concentration gradient (from low to high concentration) requires energy input from the cell (ATP).
Uses specific transport proteins embedded in the cell membrane to move specific molecules.
Examples:
Uptake of nutrients like glucose against its concentration gradient.
Removal of waste products like excess ions or toxins.

Question 10

Factors Affecting Movement

Answer 10

Concentration gradient, Size and charge of molecules, Temperature and Presence of transport proteins.

Question 11

Concentration gradient

Answer 11

The greater the difference in concentration, the faster the movement.

Question 12

Size and charge of molecules

Answer 12

Smaller and uncharged molecules move more easily.

Question 13

Temperature

Answer 13

Higher temperatures increase the kinetic energy of molecules, leading to faster movement.

Question 14

Presence of transport proteins

Answer 14

For active transport, specific proteins are needed for specific molecules.

Question 15

Effects of Solution Concentration on Plant Tissues in a Hypotonic Solution

Answer 15

Effect: Water moves into the cell due to osmosis.

Observation: Plant tissue becomes turgid (swollen and firm) as the cells take in water. This turgor pressure helps plants maintain their structure and rigidity.

Examples: Placing plant stems like celery in plain water or a dilute sugar solution.

Question 16

Effects of Solution Concentration on Plant Tissues in an Isotonic Solution

Answer 16

Effect: There is minimal net movement of water into or out of the cells.

Observation: Little to no change in the plant tissue’s overall turgor pressure or shape.

Example: This is a theoretical situation and might be difficult to achieve perfectly in an experiment. Physiological solutions like blood plasma or specific saline solutions aim to be close to isotonic for biological applications.

Question 17

Effects of Solution Concentration on Plant Tissues in a Hypertonic Solution

Answer 17

Effect: Water moves out of the cells due to osmosis.

Observation: Plant tissue becomes flaccid (limp and wilted) as the cells lose water. In severe cases, prolonged exposure can lead to plasmolysis, where the cell membrane shrinks away from the cell wall.

Examples: Placing plant tissues in concentrated salt solutions or sugar solutions.

Question 18

Explain the effects on plant tissues of immersing them in the solution of Hypotonic by using the terms turgid, turgor pressure, plasmolysis and flaccid.

Answer 18

Hypotonic Solution (Weaker): Water rushes into the cells, making them turgid (swollen and firm) due to increased turgor pressure (internal pressure). This keeps the plant upright.

Question 19

Explain the effects on plant tissues of immersing them in the solution Hypertonic by using the terms turgid, turgor pressure, plasmolysis and flaccid

Answer 19

Hypertonic Solution (Stronger): Water flows out of the cells, making them flaccid (limp and wilted). In extreme cases, excessive water loss can lead to plasmolysis, where the cell membrane shrinks away from the cell wall.

Question 20

Importance of Water Potential in Plants and Animals

Answer 20

Water potential (Ψ): This represents the free energy of water in a system, indicating its tendency to move from an area of high potential (less restricted) to an area of low potential (more restricted).

Question 21

Importance of Osmosis in Plants and Animals

Answer 21

Osmosis: The movement of water across a semi-permeable membrane (like the cell membrane) from an area of low solute concentration (high water potential) to an area of high solute concentration (low water potential).

Question 22

Importance in Plant Water Uptake

Answer 22

Plants leverage water potential and osmosis for root water uptake. Soil water, with higher potential, pushes into root cells (lower potential) due to solutes. This creates turgor pressure, keeping plants firm.

Question 23

Importance in Animal Cells and Tissues

Answer 23

Animal cells use similar principles. Osmosis regulates water balance to prevent swelling or shrinking, crucial for nutrient/waste transport and organ function (like kidneys maintaining blood pressure).

Question 24

Key differences between plant and animal cells

Answer 24

Plant cells: Can tolerate a wider range of water potential changes due to their cell walls, allowing them to maintain turgor pressure.

Animal cells: More sensitive to water potential changes due to the lack of rigid cell walls. Excessive water loss can lead to cell shrinkage (crenation) and disruption of cellular functions.