Cell Explorer

Cell Explorer

Every living thing is built from **cells**. Zoom in and you find tiny structures. Each with a job. Packed inside. This mission: tell the two cell *types* apart, name every structure and what it does, and see how cells become **specialised**. Suit up.

Two types of cell

Every cell on Earth is one of two types, and the dividing line is whether the genetic material is shut inside a nucleus or not:

Mark the claims

Five statements about the two cell types. Tap the TWO that are WRONG.

• A prokaryotic cell keeps its DNA as a loop in the cytoplasm rather than in a nucleus.
• A prokaryotic cell has no DNA at all.
• Plant and animal cells are both eukaryotic.
• Prokaryotic cells are much bigger than eukaryotic cells.
• Some bacteria carry extra small rings of DNA called plasmids.

Structures in every cell

Animal and plant cells share these sub-cellular structures. Learn the FUNCTION with the name: the exam almost always asks what a structure does rather than where it sits.

Find the control centre

Here is a plant cell. Tap the **nucleus**: the structure that controls the cell and holds its DNA.

Structures at work

A muscle cell contracts all day and needs a great deal of energy, so it contains unusually many _____. A gland cell that manufactures and exports enzymes needs large numbers of _____ instead, because that is where proteins are built. Every one of these cells is wrapped in a _____, which controls what gets in and out, and the reactions themselves take place in the _____.

Plant cells have extras

A plant cell has **everything an animal cell has, plus three more**. Each one exists because a plant faces a problem an animal does not: - **Cell wall**, made of **cellulose**. A plant has no skeleton, so the wall is what stops the cell bursting and holds the whole plant upright. - **Chloroplasts**, containing **chlorophyll**. A plant cannot go and find food, so it makes its own by **photosynthesis**. - **Permanent vacuole**, filled with **cell sap**. Pressing outwards against the wall, it keeps the cell firm (turgid), which is why a thirsty plant wilts. Note that the wall is not what controls what enters the cell: that is still the membrane's job.

Find the food factory

Tap a **chloroplast**: the plant-only structure where **photosynthesis** happens.

Why a wall?

An animal cell manages perfectly well without a cell wall. Why does a plant cell need one?

• A plant has no skeleton, so the cellulose wall stops the cell bursting and holds the plant up
• It stops water from entering the cell
• It is where photosynthesis takes place
• It stores the cell sap

Cells with a speciality

Cells are not all the same. Through **differentiation** a cell becomes **specialised**, gaining the sub-cellular structures and the shape suited to one particular job. In animals most differentiation happens **early** in development; in plants many cells keep the ability to differentiate **throughout life**. Five you should be able to describe: - **Sperm cell**: a tail to swim to the egg, and many mitochondria to power the journey. - **Nerve cell**: very long, so it can carry electrical impulses from one part of the body to another. - **Root hair cell**: a long thin projection into the soil, giving a large surface area to absorb water and mineral ions. - **Xylem cell**: dead, hollow tubes joined end to end, carrying water up the plant. - **Phloem cell**: living tubes that transport dissolved sugars around the plant.

Built for the job

A whole plant from a cutting

A gardener can grow an entire new plant from a single cutting, but a human cannot regrow a lost limb. Which difference in differentiation explains this?

• Many plant cells keep the ability to differentiate throughout life, while in animals most differentiation happens early in development
• Plant cells can divide and animal cells cannot
• Plant cells never become specialised at all
• Animals have no cells capable of differentiating at any point

Explain an adaptation

Choose ONE of these specialised cells: a **root hair cell**, a **sperm cell**, or a **nerve cell**. Explain how it is adapted to carry out its function.

• Name the cell you have chosen and say what its job is
• Describe at least TWO features of its structure
• For each feature, say HOW it helps the cell do that job, not just that it does
• Use the word "adapted" or "specialised" correctly somewhere in your answer

In the exam

A cell with a nucleus is _____; a bacterial cell has no nucleus and is _____, keeping its DNA as a loop in the cytoplasm. Every cell has a membrane, cytoplasm, ribosomes and mitochondria, and a plant cell adds a cellulose wall for support, a permanent vacuole, and _____ for photosynthesis. Through _____, a cell becomes specialised for one particular job.