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Cell & Tissues

General Science · Biology & Environment

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Overview

The cell is the basic unit of life; similar cells group into tissues that perform specific functions.

Key points

Robert Hooke observed cells in cork (1665); cell theory: Schleiden and Schwann.
Mitochondria release energy; ribosomes make proteins; the nucleus holds DNA.
Plant cells have a cell wall, chloroplasts and a large vacuole; animal cells do not.
Animal tissues: epithelial, connective, muscular, nervous.
Plant tissues: xylem carries water; phloem carries food.

Explanation

Lysosomes are "suicide bags" of the cell.
Blood and bone are connective tissues.
Meristematic tissue causes growth at root and shoot tips.
Neurons are the longest cells in the human body.

Step by step

Identify the concept or law involved.
Recall the definition, unit or formula.
Check units and the direction of the effect before choosing.

Examples

Cells were first observed by → Robert Hooke.
Water is carried in plants by → xylem.
Blood is a → connective tissue.

Traps and advanced points

Trap: Mixing xylem and phloem.
Trap: Thinking animal cells have cell walls.
Trap: Calling blood a muscular tissue.

Quick revision

Mitochondria = powerhouse.
Xylem water, phloem food.
Four animal tissues.

Practice MCQs

Concept check: What is the SI unit of energy?
1. joule
2. watt
3. newton
4. ampere
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Answer: (a) joule. Joule is the SI unit of energy.
Concept check: Which gas is released at the anode during electrolysis of acidified water under typical conditions?
1. Nitrogen
2. Hydrogen
3. Carbon dioxide
4. Oxygen
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Answer: (d) Oxygen. Oxygen is released at the anode during electrolysis of acidified water under typical conditions.
Concept check: Which pigment is primarily responsible for the green colour of plants?
1. Keratin
2. Hemoglobin
3. Melanin
4. Chlorophyll
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Answer: (d) Chlorophyll. Chlorophyll is primarily responsible for the green colour of plants.
Exam practice: Atomic number equals the number of what in an atom?
1. Electrons plus neutrons
2. Protons plus neutrons
3. Neutrons only
4. Protons
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Answer: (d) Protons. Atomic number equals the number of Protons in an atom.
Exam practice: Iodine deficiency can lead to enlargement of which gland?
1. Pancreas
2. Thyroid gland
3. Pituitary gland
4. Adrenal gland
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Answer: (b) Thyroid gland. Iodine deficiency can lead to enlargement of Thyroid gland.
Which option correctly answers this General Science check: organ that pumps blood through the body?
1. heart
2. watt
3. 3 × 10^8 m/s
4. negative charge
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Answer: (a) heart. The heart drives pulmonary and systemic circulation.
Which option correctly answers this General Science check: insulin is secreted mainly by?
1. beta cells of pancreas
2. rate of reaction
3. watt
4. vitamin K
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Answer: (a) beta cells of pancreas. Beta cells in pancreatic islets secrete insulin.
What is the SI unit of electric charge?
1. ohm
2. coulomb
3. volt
4. ampere
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Answer: (b) coulomb. One coulomb is the charge carried by one ampere in one second.
Which metal is liquid at room temperature?
1. Sodium
2. Mercury
3. Gallium
4. Lead
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Answer: (b) Mercury. Mercury is the only metal liquid at standard room temperature.
The basic unit of life is the —
1. organ
2. atom
3. tissue
4. cell
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Answer: (d) cell. The cell is the structural and functional unit of life.