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Lesson 12 of 13

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Here are the nine rules. Use the table if you get stuck.

Cell: The Building Block of Life — from one cell to a dividing one
IdeaThe rule
Everything is made of themLiving things are one cell, or many cells joined up. Viruses are not cells. The cell is the basic unit of structure and function. Every cell comes from a cell that already existed.
Inside one cellA working part inside a cell is an organelle. Each organelle has its own job. The nucleus holds the DNA. Mitochondria release energy from food.
The boundary decidesThe cell membrane lets some things pass and blocks others. This is called selective permeability. Water crosses the membrane toward the side with more dissolved substance. This movement of water is osmosis.
A plant cell and an animal cellA plant cell has a cell wall. A mature plant cell usually has one large vacuole. Green plant cells also have chloroplasts. An animal cell has no wall and no chloroplasts. Both kinds usually have a membrane, a nucleus and mitochondria.
Three kinds of plastidA plastid is a plant organelle. A chloroplast holds green chlorophyll and builds food from light. A chromoplast holds a bright pigment and colours petals and ripe fruit. A leucoplast has no pigment and stores food.
Two kinds of cellA cell with its DNA in a nucleus is eukaryotic. A cell with its DNA loose in the cytoplasm is prokaryotic. A prokaryotic cell has no membrane-bound organelles.
How big a cell can getA cell takes in materials across its surface. Double the side, and the surface grows four times. The whole cell grows eight times. So a bigger cell has less surface for its inside.
One becomes twoMitosis makes two daughter cells with the same DNA as the parent. Meiosis makes four cells with half the chromosomes. Meiosis happens only in reproductive organs.
When cells divide without controlNormal cells divide in a controlled way. Many animal cells stop dividing when they touch their neighbours. Cancer cells lose this control and keep dividing.

A sealed jar of clean syrup is opened. A week later it holds cells. Where did they come from?

  • From cells that arrived on a spoon or in the air
  • The syrup turned into cells, because sugar is food
  • They formed from the warm air in the jar

Which part releases energy from food, for the cell to use?

  • The nucleus
  • A mitochondrion
  • The cell wall

A potato piece goes into strong salt water. What happens to it?

  • It swells, because water moves in
  • It stays the same, because salt moves in
  • It shrinks, because water moves out

A green leaf cell has a part a dog's skin cell lacks. Which part?

  • A nucleus
  • A chloroplast
  • A mitochondrion

The petals of a flower are bright red. Which plastid gives the colour?

  • A chloroplast
  • A leucoplast
  • A chromoplast

A bacterial cell has DNA. Where is it?

  • Loose, in a region called the nucleoid
  • Inside a nucleus with a membrane
  • Inside a lysosome

A cell's side doubles. What happens to its surface and to all its blocks?

  • Both double
  • The surface grows 8 times, all the blocks 4 times
  • The surface grows 4 times, all the blocks 8 times

A parent cell has four chromosomes. Meiosis makes cells with how many each?

  • Four
  • Two
  • Eight

Normal cells stop dividing when they touch. What do cancer cells do?

  • They keep dividing
  • They stop too, but later
  • They die at once

This is Chapter 2, Cell: The Building Block of Life. Read it with a pencil, and work every sum yourself.

After this comes Tissues in Action. You know one cell. Next, many cells work as a team.

Reveal every answer to finish this lesson.