ExamShortcut
🔍Log in

Biology

🔒 Log in to track
high importance~2 Q in Tier 14 formulas⚡ 12 shortcuts6 subtopics
OverviewLearn (6)Formulas (4)Examples (4)Practice (120)
All subtopics·Subtopic 1 of 6

Cell, organelles and genetics

🔒 Log in to track
⏱ 4 min read🧩 6 question types🎯 18 practice Q
The idea in one minute

The cell is the basic unit of life. Each organelle inside it has one job and one nickname, such as mitochondria as the powerhouse. Cells divide by mitosis for growth and by meiosis to make gametes. Genetics adds a few names and numbers: Mendel, Watson and Crick, and 46 human chromosomes.

01

Who found what about the cell

Each scientist has one signature fact. Match the fact to the name.

DiscoveryScientist
Cell (in cork, 1665)Robert Hooke
First living cells, bacteria (single-lens microscope)Antonie van Leeuwenhoek
Nucleus (1831)Robert Brown
Cell theorySchleiden (plants) and Schwann (animals)
'Omnis cellula e cellula': new cells come from existing cellsRudolf Virchow

Watch: Hooke saw dead cork walls and named the cell. Leeuwenhoek was the first to see living cells.

02

Cell organelles

An organelle is a small working part inside the cell.

OrganelleJob or nickname
MitochondriaPowerhouse of the cell. Aerobic respiration, ATP. Has its own DNA
RibosomesProtein synthesis. No membrane
Lysosomes'Suicide bags'. Hold digestive enzymes
Golgi apparatusPackaging and secretion
Endoplasmic reticulumTransport. Rough ER (with ribosomes) makes proteins. Smooth ER makes lipids
ChloroplastPhotosynthesis. Plants only. Has its own DNA
NucleusControl centre. Holds the chromosomes (DNA)
VacuoleStorage. Large in plant cells
Cell wallPlants (cellulose) and fungi (chitin). Absent in animal cells

Tip: Four nicknames answer most questions: mitochondria = power, lysosome = suicide bag, ribosome = protein, Golgi = packing.

03

Cell types and cell records

  • Prokaryotes (bacteria, blue-green algae) have no nuclear membrane and no membrane-bound organelles.
  • Eukaryotes have a true nucleus.
  • Largest cell: ostrich egg. Longest cell: nerve cell (neuron). Smallest cell: Mycoplasma (PPLO).
  • The ovum is the largest human cell.
  • Mature mammalian RBCs have no nucleus. An RBC lives about 120 days. The spleen removes worn-out RBCs.
04

Cell division

MitosisMeiosis
PurposeBody growth and repairMakes gametes
Cells formed2 identical cells4 cells
Chromosome numberStays the sameHalved

Take a human cell. Mitosis keeps 46. Meiosis gives 23 in each gamete.

05

Genetics basics

  • Gregor Mendel is the father of genetics. He worked on the garden pea (Pisum sativum).
  • His laws are dominance, segregation and independent assortment.
  • DNA double helix: Watson and Crick (1953), using X-ray data of Rosalind Franklin and Maurice Wilkins.
  • DNA bases are A, T, G, C. RNA has uracil in place of thymine.
06

Human chromosomes and inheritance

Body cells hold 46 chromosomes (23 pairs). That is 22 pairs of autosomes plus 1 pair of sex chromosomes. Gametes hold 23.

Rule: The father decides the sex of the child. XX is female. XY is male.

  • Haemophilia and colour blindness are X-linked. They are more common in males.
  • Down syndrome is an extra chromosome 21 (trisomy 21).
07

Theories and names to know

  • Hugo de Vries: mutation theory.
  • Darwin: natural selection (On the Origin of Species, 1859).
  • Lamarck: inheritance of acquired characters.
  • Har Gobind Khorana: Nobel Prize 1968 for work on the genetic code.
08

Question types you will see

Each type: how to recognise it, the method step by step, and one question to try.

Type 1very common3 practice Q

Cell theory and discoverers

How to spot it:

Words like 'who discovered the cell / nucleus / living cells', 'cell theory', 'omnis cellula e cellula', or a year (1665, 1831).

Method

  1. Read the noun: cell, living cell, nucleus or theory.

  2. Match it to its one scientist from the table.

  3. Use the year to break ties: 1665 Hooke, 1831 Brown.

Why it works:

Each scientist has exactly one signature fact.

Try this

The cell theory was proposed by which pair of scientists?

Show solution

  1. Theory means Schleiden (plants) and Schwann (animals).

  2. Hooke only named the cell.

  3. Virchow added that cells come from cells.

Answer

Schleiden and Schwann

Type 2very common3 practice Q

Organelle and its function or nickname

How to spot it:

'Powerhouse of the cell', 'suicide bags', 'which organelle makes protein', 'which organelle has its own DNA'.

Method

  1. Find the nickname or job in the question.

  2. Recall the pair from the organelle table.

  3. For own DNA, choose mitochondria or chloroplast.

Why it works:

The question is always one nickname or one job.

Try this

Which organelle is called the 'suicide bag' of the cell?

Show solution

  1. Suicide bag means it digests the cell itself.

  2. Lysosomes hold digestive enzymes.

Answer

Lysosome

Type 3common2 practice Q

Prokaryote vs eukaryote, plant vs animal cell

How to spot it:

'Which is a prokaryote', 'no true nucleus', 'cell wall is made of', 'absent in animal cells'.

Method

  1. Bacteria and blue-green algae are prokaryotes. Everything else is eukaryote.

  2. Cell wall, chloroplast and large vacuole mark plant cells.

  3. For 'absent in animal cells', pick cell wall or chloroplast.

Why it works:

Prokaryotes lack a nuclear membrane and membrane-bound organelles.

Try this

The cell wall of a plant cell is made of what?

Show solution

  1. Plants use cellulose in the wall.

  2. Fungi use chitin.

Answer

Cellulose

Type 4common2 practice Q

Cell division and chromosome numbers

How to spot it:

'Chromosomes in a human body cell', 'chromosomes in a gamete', 'mitosis vs meiosis', 'which division keeps the number the same'.

Method

  1. Body cell: 46. Gamete: 23.

  2. Growth and repair means mitosis: the number stays.

  3. Gamete formation means meiosis: the number halves.

Why it works:

Meiosis halves the number so fertilisation can restore it.

Try this

A human gamete contains how many chromosomes?

Show solution

  1. A body cell has 46.

  2. Meiosis halves it: 46 / 2 = 23.

Answer

23

Type 5common4 practice Q

Genetics: Mendel, DNA and inheritance

How to spot it:

'Father of genetics', 'DNA double helix', 'Mendel worked on which plant', 'who decides the sex of a child'.

Method

  1. Match the name to its one fact.

  2. Mendel is the garden pea. Watson and Crick is 1953.

  3. Sex: the mother always gives X. The father gives X or Y.

Why it works:

One name, one organism and one year make up the whole question.

Try this

Watson and Crick are famous for which work?

Show solution

  1. Their year is 1953.

  2. They built the model of DNA.

Answer

The double-helix model of DNA

Type 6common2 practice Q

Blood cells and cell records

How to spot it:

'Which blood cells lack a nucleus', 'lifespan of RBC', 'largest / longest cell', 'which cell carries oxygen'.

Method

  1. RBC has no nucleus, carries oxygen and lives about 120 days.

  2. WBC defends. Platelets clot the blood.

  3. Records: ovum is the largest human cell. Nerve cell is the longest.

Why it works:

Each blood cell has one job.

Try this

What is the average lifespan of a human red blood cell?

Show solution

  1. RBCs live about 120 days.

  2. The spleen removes worn-out RBCs.

Answer

About 120 days

09

Shortcuts that save time

⚡ Organelle nicknames: Power-Mito, Suicide-Lyso, Protein-Ribo, Packing-Golgi

These four nicknames answer most organelle questions.

Example

Which organelle is called the 'suicide bag' of the cell?

Show solution

  1. Suicide points to self-digestion.

  2. Lysosomes hold digestive enzymes.

Answer

Lysosome.

⚡ Cell discoverers in order

Hooke saw the cell (1665, dead cork). Leeuwenhoek saw it alive. Brown saw the nucleus. Schleiden and Schwann made the theory. Virchow said cells come from cells.

10

Mistakes to avoid

Where most students lose marks on this subtopic.

Mistake 01

Saying Leeuwenhoek discovered the cell.

Hooke named the cell. Leeuwenhoek first saw living cells.

Mistake 02

Saying the mother decides the child's sex.

The father decides it. His sperm carries X or Y.

Mistake 03

Giving animal cells a cell wall.

Only plants, fungi and bacteria have one.

Mistake 04

Thinking meiosis makes two identical cells.

Mitosis gives 2 identical cells. Meiosis gives 4 cells with half the chromosomes.

Mistake 05

Saying every cell has a nucleus.

Prokaryotes have none. Mature mammalian RBCs have none.

11

Quick revision

Read this the night before the exam.

  • Hooke 1665 cork; Leeuwenhoek living cells; Brown nucleus 1831; Schleiden-Schwann theory; Virchow: cells from cells.

  • Mitochondria: powerhouse. Lysosome: suicide bag. Ribosome: protein. Golgi: packaging.

  • Cell wall: cellulose in plants, chitin in fungi. Absent in animal cells.

  • Largest cell: ostrich egg. Longest: neuron. Smallest: Mycoplasma.

  • Mitosis: 2 identical cells. Meiosis: gametes, chromosomes halved.

  • Human: 46 chromosomes (23 pairs). Gamete: 23. Father decides sex.

  • Mendel: pea. Watson and Crick: DNA 1953. Down syndrome: trisomy 21.

12

Practice: 18 questions

Sets of 10, mixed across the question types above. Every answer has a step-by-step explanation.

Topic test · 10 questions

Suggested time 3 min · wrong answers go to your mistake notebook automatically.

Continue learning