Question
▶️Answer/Explanation
Question
What distinguishes simple diffusion from facilitated diffusion?
A. Simple diffusion occurs in both prokaryotes and eukaryotes, while facilitated diffusion only occurs in eukaryotes.
B. Energy is not required for simple diffusion, while facilitated diffusion requires ATP.
C. The rate of facilitated diffusion depends on the number of transport proteins in the membrane, while simple diffusion does not.
D. Simple diffusion can only move substances along the concentration gradient, while facilitated diffusion can move substances along or against the concentration gradient.
▶️Answer/Explanation
Ans: C
Question
The diagrams illustrate the molecular structure of carbon compounds found in living organisms. Which of these is present in phospholipids?
▶️Answer/Explanation
Ans. A
A- the given compound is fatty acid chain
- Glycerol: The chemical formula for glycerol is CH2OCHOCH2O
- Fatty acid chains: These chains are made up of 3–30 or more CH groups and can be saturated or unsaturated
- Phosphate group: The chemical formula for the phosphate group is PO4Phospholipids are amphipathic molecules, meaning they have both hydrophobic and hydrophilic components:
- Phosphate headThe phosphate group is negatively charged, making the head polar and hydrophilic, or “water loving”
- Lipid tails
The lipid tails are uncharged, nonpolar, and hydrophobic, which means they are “water fearing”
Question
What accounts for the movement of glucose molecules across the cell surface membrane down a concentration gradient?
A. They can diffuse between phospholipids due to their flexibility.
B. They are actively transported by protein pumps due to their size.
C. They move through hydrophilic channels because they are polar.
D. They dissolve in the phospholipid bilayer because they are not charged.
▶️Answer/Explanation
Ans. C
Facilitated diffusion is the process that allows glucose molecules to move across a cell membrane down a concentration gradient:
Facilitated diffusion is a type of passive transport that uses carrier proteins or pores in the membrane to move molecules from a high concentration to a low concentration. This process doesn’t require energy because the molecules move along the concentration gradient.
Glucose transporters (GLUTs) are carrier proteins that facilitate the diffusion of glucose across cell membranes. There are several isoforms of GLUTs, including GLUT1-5.
The activity of glucose transporters is affected by metabolic stresses, such as hypoxia, injury, hypoglycemia, and stress hormones. Chronic low-grade inflammation and chronic diseases like obesity, type 2 diabetes, and cardiovascular disease can also alter glucose transport.
Question
The diagram illustrates the fluid mosaic model of cell membranes. Which labeled areas are hydrophilic?
A. I and II
B. I and III
C. II and IV
D. III and IV
▶️Answer/Explanation
Ans. D
The hydrophilic components of the cell membrane are the heads of the phospholipids, proteins, and carbohydrates:
The main structural component of the cell membrane, phospholipids are amphipathic molecules, meaning they have both hydrophilic and hydrophobic parts. The hydrophilic heads of phospholipids are attracted to water, while the hydrophobic tails are repelled by water. The arrangement of phospholipids in the cell membrane creates a selectively permeable barrier.
Integral proteins span the entire cell membrane and contain both hydrophilic and hydrophobic regions. They often act as transport proteins, moving molecules and ions across the membrane.
Amphiphilic components of the cell membrane, glycolipids have a hydrophilic polar sugar headgroup and a hydrophobic apolar lipid moiety.
Question
By which process do potassium ions move through potassium channels in axons?
Active transport
Exocytosis
Facilitated diffusion
Simple diffusion
▶️Answer/Explanation
Ans: C
Facilitated diffusion of potassium is a process by which potassium ions move through potassium channels in axons. Potassium channels are integral proteins with a hydrophilic inner pore that allow potassium ions to pass through. This process does not require energy and is driven by the concentration gradient of potassium ions across the membrane. Facilitated diffusion of potassium is important for the transmission of electrical impulses by nerve cells.
The diagram is a model of one type of movement across a membrane.
What is this type of movement?
A. Simple diffusion
B. Facilitated diffusion
C. Osmosis
D. Active transport
▶️Answer/Explanation
Markscheme
B
Facilitated diffusion is a type of passive transport that allows substances to move across a cell membrane with the help of transport proteins. It is a selective process, meaning that only certain molecules and ions can pass through the membrane. This process does not require energy from ATP hydrolysis.
What features of a cell favour efficient removal of waste products?
▶️Answer/Explanation
Markscheme
B
The surface area to volume ratio (SA:V) of a cell affects how efficiently it can remove waste products.
The higher the SA:V, the easier it is for the cell to exchange substances with its environment. This is because a high SA:V means that the cell has more surface area relative to its volume, so it can diffuse more substances across its membrane per unit of time.
A low SA:V means that the cell has less surface area relative to its volume, so it can diffuse fewer substances across its membrane per unit of time. This can limit the cell size, because if the cell grows too large, its metabolic rate may exceed the rate of exchange of vital materials and wastes. The cell may not be able to get enough nutrients and oxygen, or get rid of carbon dioxide and waste materials fast enough.
Therefore, a high SA:V can favor efficient removal of waste products by allowing faster diffusion across the cell membrane. A low SA:V can hinder efficient removal of waste products by slowing down diffusion across the cell membrane.
The salt concentration inside the Paramecium is 1.8 %. The salt concentration in the surrounding medium suddenly drops to 0.2 %. What will be the likely response?
A. The cell will lose salt to the medium.
B. The contractile vacuole will expel more water.
C. The cell will swell and eventually burst.
D. The membrane will become more permeable to salt.
▶️Answer/Explanation
is the correct answer.
When the salt concentration outside the cell suddenly drops, water will move into the cell by osmosis, causing the cell to swell. To prevent the cell from bursting, the contractile vacuole will expel more water from the cell.
This process of expelling excess water from the cell is known as osmoregulation, and it is the correct response to a sudden drop in salt concentration in the surrounding medium.