Chapter 2: Movement of substances 🌬️

Question 1

What is matter made up of?

Answer 1

• All matter is made up of particles such as atoms, molecules, and ions.

Question 2

What is a fluid made up of?

Answer 2

• Fluids such as liquids and gases are made up of particles that are constantly moving in a random manner.
• Hence diffusion can take place.

Question 3

What does it mean by concentration/the concentration of a substance/matter?
OR
What is concentration?

Answer 3

• Concentration is the amount of substance in a fixed volume

Question 4

What is a concentration gradient?

Answer 4

• A concentration gradient is the difference in the concentration between 2 regions.

Question 5

Why do all particles have a natural tendency and why is it so important?

Answer 5

• All particles have a natural tendency to move down their concentration gradient and become evenly spaced out after some time.

Question 6

What is diffusion?

Answer 6

• Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration down a concentration gradient.

Question 7

What is a permeable membrane?
OR
Why is a permeable membrane so important?

Answer 7

• A permeable membrane allows particles of all sizes to pass through freely.
• Thus, it allows both concentrations to be in equilibrium.

Question 8

What is an example of diffusion in the respiratory system of a human?

Answer 8

RESPIRATORY SYSTEM:
- Diffusion of oxygen from the alveoli to red blood cells.
- Diffusion of carbon dioxide from the blood to the alveoli.

Question 9

What is an example of diffusion in the digestive system of a human?

Answer 9

• Absorption of digested food from the small intestine to the blood capillaries.
• (Unsure about this point): Diffusion of waste substances from the tissue cells into the blood capillaries to be passed out from the body.

Question 10

What is an example of diffusion in the respiratory system of a plant?

Answer 10

• The entry of oxygen from spaces in the soil into the root hair cells
• The removal of carbon dioxide from the root hair cells.

Question 11

What is an example of diffusion in the photosynthetic system of a plant?

Answer 11

• The movement of oxygen from the leaves to the external environment.
• The entry of carbon dioxide from the external environment into the leaves. (during photosynthesis ☀️🌱)

Question 12

What does it mean by “surface area-to-volume ratio”?

Answer 12

• Surface-area-to-volume ratio refers to how much surface area an object has per unit volume.
• The size of a cell is limited by its surface area-to-volume ratio.

Question 13

What happens when the volume of the cell increases?

Answer 13

• As the volume of a cell increases, the corresponding increase in its surface area is not the same (because as the volume of the cell increases, the surface area-to-volume ratio decreases).
• This decreases the surface area-to-volume ratio which decreases the rate of diffusion of particles across the cell.
• Substances cannot diffuse in and out of a larger cell fast enough to support its metabolic activities.
  Q: What does it mean by that?
  A: Due to the larger size of the cell, it takes a longer time for substances to diffuse in and out of the cell, compared to a smaller cell, where less time is taken for substances to diffuse in and out of the cell.
• When substances cannot diffuse in and out of a larger cell fast enough to support its metabolic activities, it means that the cell is not receiving enough nutrients or oxygen to function properly. This can lead to a buildup of waste products and a decrease in the cell’s energy production.
• The cell membrane is selectively permeable, meaning that it allows some substances to pass through while blocking others, which depends on their size and the membrane’s pore size.
• Some molecules can move down their concentration gradients by crossing the lipid portion of the membrane directly, while others must pass through membrane proteins in a process called facilitated diffusion.
• Very large molecules such as proteins are too big to move through the cell membrane, thus the cell membrane is impermeable to the proteins.
  (E.g. Larger molecules such as glucose require a specific transport protein to facilitate their movement across the cell membrane.)

Question 14

What are the factors that affect the rate of diffusion?

Answer 14

1. Concentration gradient
   - The steeper the concentration gradient, the faster the rate of diffusion.
2. Surface area-to-volume ratio
   - The larger the surface area-to-volume ratio, the greater the area for substances to pass through and hence, the faster the rate of diffusion.
3. Diffusion distance
   - The shorter the distance, the less time needed for the substance to travel. Thus, the faster the rate of diffusion.

Question 15

Why do cells have modified shapes to ensure efficient rates of diffusion?

Answer 15

• Cells involved in transportation have modified shapes with a high surface area-to-volume ratio to ensure efficient rates of diffusion.
  -E.g. A root hair cell –> Has a long protrusion.
  Epithelial cells –> Have microvilli.
  red blood cells –> Are flattened and have a biconcave shape to increase the amount of surface area for the absorption of nutrients and the diffusion of substances.

Question 16

What is osmosis?

Answer 16

• 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. (via osmosis)

Question 17

What is water potential?

Answer 17

• Water potential is the tendency for water molecules to move from one region to another.

Question 18

How does the water molecules move through solutions?

Answer 18

• Water molecules move from a dilute solution to a concentrated solution.
  Reasoning:
  1. This is because a dilute solution has a greater number of water molecules than a concentrated solution, thus it has a higher water potential than a concentrated solution. (DILUTE SOLUTION)
  2. This is because a concentrated solution has a smaller number of water molecules than a dilute solution, thus it has a lower water potential than a dilute solution. (CONCENTRATED SOLUTION)

Question 19

What is a water potential gradient?

Answer 19

• A water potential gradient is the difference in water potential between 2 bodies of liquids.
• E.g., Distilled water has the highest water potential of any solution as it is made up of 100% water molecules.

Question 20

What is a partially permeable membrane?

Answer 20

• A partially permeable membrane is a membrane that allows smaller particles to pass through, but it prevents larger particles from passing through.

Question 21

What is an example of diffusion in the transport system of a human?

Answer 21

• The movement of water molecules into cells from the tissue fluid.

Question 22

What is an example of diffusion in the excretory system of a human?

Answer 22

• The absorption of water in the kidneys.

Question 23

What is an example of diffusion in the transport system of a plant?

Answer 23

• Transportation of water from cell to cell, and up to the leaves for photosynthesis.

Question 24

Why do plant and animal cells behave differently in solutions of varying water potential?

Answer 24

• Plant and animal cells behave differently in solutions of varying water potential due to the presence or absence of a cell wall (respectively).

Question 25

What happens in a solution with a higher water potential than the cytoplasm?

Answer 25

• In a solution with a higher water potential (more diluted–> decreased concentration) than the cytoplasm, water molecules move into the cell via osmosis which causes the cell to swell. Thus, it may enlarge in size.
  *: More diluted –> Decreased concentration.
  Less diluted –> Increased concentration.
  More concentrated (lesser water molecules) –> Increased concentration. ❓
  Less concentrated (more water molecules) –> Decreased concentration.❓

Question 26

What are some examples of osmosis in a plant cell when water molecules enter the cell?

Answer 26

1. the vacuole expands and pushes the cytoplasm against the cell wall.
2. The plant cell then becomes turgid, but it does not burst as it is protected by the cell wall.
3. The pressure exerted by the water in the vacuole is turgor pressure.

Question 27

What is turgor pressure?

Answer 27

• Turgor pressure is the pressure exerted by the water in the vacuole.
  Steps:
  1. Water molecules enter the cell by osmosis.
  2. The cell becomes turgid and does not burst.

Question 28

What are some examples of osmosis in an animal cell when water molecules enter the cell?

Answer 28

1. The cell membrane bursts when water pressure binds up due to the absence of a cell wall.
   Steps:
2. Water molecules enter the cell by osmosis.
3. The cell expands and bursts (burst in terms of water molecules).

Question 29

What happens in a solution with a lower water potential than the cytoplasm?

Answer 29

• In a solution with a lower water potential (more concentrated) than the cytoplasm, water molecules move out of the cell via osmosis, this causes the cell to shrink.

Question 30

What are some examples of osmosis in a plant cell when water molecules leave the cell via osmosis?

Answer 30

• In a plant cell, the vacuole shrinks, and the cell membrane pulls away from the cell wall when water molecules leave the cell.
• This process is known as PLASMOLYSIS, the plant cell then becomes limp (flaccid) and is said to be plasmolysed (a term/condition).

Question 31

What is PLASMOLYSIS?

Answer 31

• PLASMOLYSIS is a process whereby the vacuole in a plant cell shrinks and the cell membrane pulls away from the cell wall when water molecules leave the cell.
  Steps:
  1. Water molecules leave the cell by osmosis,
  2. The cell becomes plasmolysed and flaccid.

Question 32

What are some examples of osmosis in an animal cell when water molecules leave the cell via osmosis?

Answer 32

• In an animal cell, spikes appear on the cell membrane when water molecules leave the cell. This is due to CRENATION (a process), and the cell will eventually die.
  Steps:
  1. Water molecules leave the cell via osmosis.
  2. The cell becomes CRENATED and eventually dies, this is due to the gradual reduction of water molecules in the cell till there is no more water left. (whole cell becomes dry and brittle –> dies)

Question 33

What are the factors that affect the rate of osmosis?

Answer 33

1. Water potential gradient:
   (How it affects the rate of osmosis):
   - The steeper the water potential gradient, the faster the rate of osmosis.
   - The less steep the water potential gradient, the slower the rate of osmosis.
2. Surface area-to-volume ratio:
   (How it affects the rate of osmosis):
   - The larger the surface area-to-volume ratio, the greater the area for water molecules to pass through. Hence, the faster the rate of osmosis.
   - The smaller the surface area-to-volume ratio, the smaller the area for water molecules to pass through. Hence, the slower the rate of osmosis.
3. Distance in which water molecules need to move:
   (How it affects the rate of osmosis):
   - The longer the distance, the more time needed for water molecules to travel. Hence, the slower rate of osmosis.
   - The shorter the distance, the less time needed for water molecules to travel. Hence, the faster rate of osmosis.

Question 34

What is turgor pressure?

Answer 34

• Turgor pressure refers to the pressure that is exerted by the fluid against the cell wall.
• As water fills the cells, it pushes against the cell membrane and the cell wall, producing turgor pressure.
• Turgor pressure is essential for the plant’s vital processes as it makes the plant cell stiff and rigid. Without turgor pressure, the plant cell becomes flaccid.
• Prolonged flaccidity could lead to the wilting of plants.
  -Turgor pressure is also important in stomate (A term for microscopic opening or pores in the epidermis of leaves and young stems) formation.
• The turgid guard cells create an opening for gas exchange. Carbon dioxide could enter and be used for photosynthesis.

Question 35

Why is TURGOR important in plant cells?

Answer 35

• Turgor is important in plant cells because the TURGOR PRESSURE within the plant cells allows the stems and leaves of non-woody plants to stay firm and erect.
• So, when the plant cells lose their turgor, the plant wits.
• The change in turgor causes the movement of certain plant parts. (E.g.) The opening and closing of stomata are due to the changes in the turgor of the guard cells.

Question 36

What is active transport?

Answer 36

• Active transport is the process in which energy is used to move particles across a membrane from a region of lower concentration to a region of higher concentration against a concentration gradient.

*- (lower concentration –> higher concentration)

Question 37

Why do cells that are involved in active transport have abundant amounts of mitochondria?

Answer 37

• This is because the cells involved in active transport have abundant mitochondria to provide the required energy for cellular processes. (e.g.) Growth, tissue repair, etc…

Question 38

What are the examples of active transport in the excretory system of a human?

Answer 38

• The reabsorption of glucose (carbohydrates) and amino acids (proteins) in the kidneys.

Question 39

What are the examples of active transport in the transport system of a plant?

Answer 39

• The uptake (absorption) of mineral salts by the root hair cells from the soil.
• Transportation of sucrose (a type of sugar) from photosynthetic leaves to the other parts of the plant through the phloem.

Question 39

What are the examples of active transport in the digestive system of a human?

Answer 39

• The uptake (absorption) of glucose by microvilli (very small villis) in the small intestine.