Smaller, lipid soluble molecules diffuse faster through cell membrane, but the movement of hydrophilic substances is facilitated by certain transporters which are chemically

Proteins

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Carbohydrates

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Lipids

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Phospholipids

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Solution

The correct option is B Proteins
Particles which are lipid soluble (i.e., lipophilic or hydrophilic) can easily diffuse through the cell membrane as the lipid is a major constituent of the membrane. Where as hydrophilic substances (i.e., the substances which are soluble in water, e.g., glucose) do not pass through a biological membrane by simple diffusion. They are, therefore, transported across a cell membrane by facilitated diffusion (i.e., carrier mediated diffusion), which takes place with the help of certain transport proteins. So, the correct answer is 'Proteins'.

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Similar questions

Q. Short / Long answer type questions.
Why do most substances have to be assisted through the plasma membrane? Contrast movement by facilitated transport with movement by active transport.

Q. Facilitated diffusion requires protein channels to transport molecules across a membrane but does not require a concentrantion gradient.

The following list indicates certain molecules/ions and their mechanism of transport across the cell membrane. Determine the correct pair(s) from the list.

I. Diffusion - $N a^{+}$

II. Active transport - Amino acids

III. Osmosis - Water

IV. Facilitated diffusion - Glucose

Hydrophilic molecules cannot diffuse across the plasma membrane.

Question 29
Select the odd one out

(a) The movement of water across a semi-permeable membrane is affected by the amount of substances dissolved in it.
(b) Membranes are made of organic molecules like proteins and lipids
(c) Molecules soluble in organic solvents can easily pass through the membrane.
(d) Plasma membranes contain chitin sugar in plants

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