Which one among the following statements about facilitated transport in plants is correct?
- A.All passive transports are types of facilitated transport.
- B.Facilitated transport is an example of active transport.
- C.Water moves across plasma membrane by active transport.
- D.Facilitated transport requires assistance of carrier proteins.
Correct answer
Explanation
The correct answer is D, Facilitated transport requires assistance of carrier proteins. In facilitated transport, molecules cross the membrane with the help of membrane proteins, while still moving down their concentration gradient.
Substances that dissolve in fats, such as oxygen and carbon dioxide, pass through the lipid layer of the membrane by simple diffusion. Polar molecules and ions, such as sugars and amino acids, cannot cross the lipid layer on their own, so carrier proteins or channel proteins provide a route. Because they move from higher to lower concentration, this needs no energy from ATP, so facilitated transport is a kind of passive transport. Active transport, by contrast, uses ATP to move substances against their gradient, as the sodium-potassium pump does.
A is wrong because simple diffusion is passive but needs no proteins, so not all passive transport is facilitated. B is wrong because facilitated transport uses no energy and is passive. C is wrong because water crosses the membrane passively by osmosis, partly through channel proteins called aquaporins.
Exam tip: simple diffusion = no protein; facilitated diffusion = protein, no energy; active transport = protein and ATP.
Practice Questions
View allWhich of the following are nitrogen-fixing plants?
1. Alfalfa
2. Amaranth
3. Chickpea
4. Clover
5. Purslane (Kulfa)
6. Spinach
Select the correct answer using the code given below:
- A.1, 3 and 4 only
- B.1, 3, 5 and 6 only
- C.2, 4, 5 and 6 only
- D.1, 2, 4, 5 and 6
Show answer
Alfalfa, chickpea and clover are legumes, and legumes fix nitrogen. Plants of the legume family (Fabaceae) carry root nodules that house Rhizobium bacteria.
Read the full explanation →The mass number of an element is NOT changed when it emits
- A.Alpha and Beta radiations only
- B.Alpha and Gamma radiations only
- C.Beta and Gamma radiations only
- D.Alpha, Beta and Gamma radiations
Show answer
Neither beta nor gamma emission changes the total number of protons and neutrons in a nucleus, so the mass number stays the same.
Read the full explanation →Who among the following has coined the term 'Quark', the fundamental particles that make up protons and neutrons in an atomic nucleus ?
- A.Richard Feynman
- B.Murray Gell-Mann
- C.Albert Einstein
- D.Niels Bohr
Show answer
The American physicist Murray Gell-Mann proposed quarks in 1964 and gave them their name. Gell-Mann, and independently George Zweig, suggested that protons, neutrons and other such particles are built from smaller units.
Read the full explanation →The spindle fibre is attached to which of the following specific regions of the chromosomes?
- A.Kinetochore
- B.Chromonema
- C.Telomere
- D.Centriole
Show answer
Spindle fibres attach to the kinetochore, a disc-shaped protein structure on the centromere of each chromosome. During cell division the spindle, made of microtubules, pulls the copies of each chromosome apart.
Read the full explanation →Which one of the following is the chemical name of heavy water?
- A.Hydrogen oxide
- B.Deuterium dioxide
- C.Deuterium oxide
- D.Heavy hydrogen oxide
Show answer
Heavy water is D₂O: two atoms of deuterium joined to one atom of oxygen. Deuterium is the isotope of hydrogen with one proton and one neutron in its nucleus, so it is about twice as heavy as ordinary hydrogen.
Read the full explanation →