GCSE Biology Cell Biology 2 — Questions and Answers
Question 1: Which of these is an example of active transport?
- Oxygen moving from the alveoli into the blood
- Root hair cells absorbing mineral ions from dilute soil water (Correct answer)
- Water entering a plant cell placed in pure water
- Carbon dioxide leaving a leaf through the stomata
Correct answer: Root hair cells absorbing mineral ions from dilute soil water
Mineral ions are absorbed by root hairs against their concentration gradient using energy.
Soil water usually contains a lower concentration of mineral ions than the inside of a root hair cell. To absorb them, the cell must move ions against the concentration gradient, which requires energy released by respiration. This is active transport. The other examples all occur passively down a concentration gradient by diffusion or osmosis.
Question 2: During which stage of the cell cycle do the chromosomes get pulled to opposite ends of the cell?
- Cytokinesis
- Interphase
- DNA replication
- Mitosis (Correct answer)
Correct answer: Mitosis
In mitosis, one set of chromosomes is pulled to each end of the cell before it divides.
The cell cycle has three main stages. In interphase the cell grows, increases its number of sub-cellular structures and replicates its DNA. In mitosis, one set of chromosomes is pulled to each end of the cell and the nucleus divides. Finally, the cytoplasm and cell membrane divide to form two genetically identical daughter cells.
Question 3: What is a stem cell?
- A cell that has lost its nucleus
- An undifferentiated cell that can divide to produce many more cells of the same type or differentiate into specialised cells (Correct answer)
- A specialised cell found only in plant stems
- A cell that can only divide by meiosis
Correct answer: An undifferentiated cell that can divide to produce many more cells of the same type or differentiate into specialised cells
Stem cells are undifferentiated cells capable of dividing and becoming specialised.
A stem cell is an undifferentiated cell of an organism which is capable of giving rise to many more cells of the same type, and from which certain other cells can arise by differentiation. Human embryonic stem cells can become almost any type of cell, while adult stem cells (e.g. in bone marrow) are more limited. Plant meristem cells behave like stem cells throughout the life of the plant.
Question 4: Which adaptation of a sperm cell helps it to swim to the egg?
- Many chloroplasts
- A large permanent vacuole
- A tail (flagellum) (Correct answer)
- A thick cellulose cell wall
Correct answer: A tail (flagellum)
The tail allows the sperm cell to swim towards the egg.
Sperm cells are specialised for reproduction. They have a long tail (flagellum) for swimming, many mitochondria to release the energy needed for movement, and an acrosome containing enzymes to digest the outer layer of the egg. Chloroplasts, vacuoles and cellulose cell walls are plant cell features.
Question 5: Which of the following correctly describes diffusion?
- The net movement of particles from an area of higher concentration to an area of lower concentration (Correct answer)
- The movement of water only across a partially permeable membrane
- The movement of particles from low to high concentration using energy
- The movement of particles only through a cell wall
Correct answer: The net movement of particles from an area of higher concentration to an area of lower concentration
Diffusion is the spreading out of particles from high to low concentration.
Diffusion is the spreading out of the particles of any substance in solution, or particles of a gas, resulting in a net movement from an area of higher concentration to an area of lower concentration. It is a passive process. Factors that increase the rate of diffusion include a steeper concentration gradient, a higher temperature and a larger surface area.
Question 6: Why do multicellular organisms need exchange surfaces and transport systems?
- Because their cells contain no mitochondria
- Because they have a large surface area to volume ratio
- Because they have a small surface area to volume ratio, so diffusion alone is too slow (Correct answer)
- Because their cell membranes are fully permeable
Correct answer: Because they have a small surface area to volume ratio, so diffusion alone is too slow
Large organisms have a small surface area to volume ratio, so diffusion is insufficient.
As an organism gets larger, its volume increases faster than its surface area, so the surface area to volume ratio decreases. This means diffusion across the outer surface cannot supply all the cells fast enough. Multicellular organisms therefore have specialised exchange surfaces (like alveoli and villi) and transport systems (like the blood) to move substances efficiently.
GCSE Biology Cell Biology 2
Which of these is an example of active transport?