Chapter 2 of igcse book biolgy ,learning ,science ,biolgy ,igcse ,english ,learning ,science ,biolgy ,igcse ,english ,learning ,science ,biolgy ,igcse ,englishI

1. CELLS

2. Microscopes
● To see cells clearly, you need to use a microscope.
● The kind of microscope used in a school is called a light microscope.
The light microscope magnifies up to x 1500.

3. An electron microscope magnifies up to x 10 millions.

6. Cell membrane
● All cells have a cell membrane.
● The cell membrane is a very thin layer of protein and fat.

7. ● The cell membrane controls what goes in and out of it.
● It is said to be partially permeable, which means that it will let some
substances through but not others.

8. Cell wall
● All plant cells surrounded by a cell wall made mainly of cellulose.
● Cell wall protect and support the cell.

9. Cytoplasm
● All cells have a cytoplasm.
● It is mainly composed of water in many cells.
● Many different metabolic reactions take place in the cytoplasm.

10. Vacuoles
● A vacuole is a space in a cell, surrounded by a membrane, and containing a
solution.
● Plant cells have large vacuoles, which contain sugar and other subtances
called cell sap.
● Animal cells have much smaller spaces called vesicles which may contain
food or water.

12. Chloroplast
● They contain the green colouring pigment called chlorophyll.
● Chlorophyll absorbs energy from sunlight and this energy is then used for
photosynthesis.

13. ● Chloroplasts store starch grains which have been made by photosynthesis.
● Animal cells also have grains similar to starch,called glycogen inside
cytoplasm.

14. Nucleus
● The nucleus is where the genetic information is stored.
● The information kept on the chromosomes,which are inherited from the
organism’s parents. The chromosomes made of DNA.

15. Mitochondria
● Almost all cells except prokaryotes have mitochondria.

16. ● Mitochondria are the powerhouses of the cell.
● Aerobic respiration occurs in mitochondria
● Cells that use a lot of energy have a lot of mitochondria.(muscle cells, sperm
cells, neurons)

17. Ribosomes
● Ribosomes are found in all types of cells (bacteria,fungi,animal,plant...)
● Ribosomes are the places where proteins are made.
● They are found in many places around a cell. You might find them floating in
the cytoplasm.

18. ● Other ribosomes are found on the endoplasmic reticulum. Endoplasmic
reticulum with attached ribosomes is called rough ER.

19. Micrometres
● Cells, and structures inside them such as mitochondria and ribosomes, are so
small that we need a very small unit in which to measure them. The most
useful one is the micrometre (µm).
● 1µm = 1 x 10-6 m
● 1 m = 1 x 106 µm

20. Adaptations of Specialised Cells
● Specialised cells are those which have developed certain characteristics in order to
perform particular functions. These differences are controlled by genes in the nucleus.
● Cells specialise by undergoing differentiation: this is a process by which cells develop
the structure and characteristics needed to be able to carry out their functions.
Examples of Specialised Cells in Animals:
★ ciliated cell
★ nerve cell
★ red blood cell
★ sperm cell
★ egg cell (ovum)
Examples of Specialised Cells in Plants:
★ root hair cell
★ xylem vessel
★ palisade mesophyll cell

21. Ciliated cells

22. Nerve cell

23. Red blood cells

24. Sperm cell

25. Egg cell (ovum)

26. Root hair cell

27. Xylem

28. Palisade mesophyll cell

29. Cells and organisms
● Cell : the smallest unit of life
● Tissue : an aggregate of cells in an
organism that have similar structure
and function.
● Organ : a group of tissues that perform
a specific function or group of
functions.
● Organ System : A group of entities or
organs that work together to carry out a
particular task

32. Calculating Magnification & Specimen Size
Calculating magnification and specimen size using millimetres as units
● Magnification is calculated using the following equation:
Magnification = Drawing size ÷ Actual size
A better way to remember the equation is using an equation triangle:

33. ● Rearranging the equation to find things other than the magnification becomes easy
when you remember the triangle – whatever you are trying to find, place your finger
over it and whatever is left is what you do, so:
○ Magnification = image size / actual size
○ Actual size = image size / magnification
○ Image size = magnification x actual size
● Remember magnification does not have any units and is just written as ‘x 10’ or ‘x
5000’

34. An image of an animal cell is 30 mm in size and it has been magnified by a factor of x 3000. What is
the actual size of the cell?
To find the actual size of the cell:

35. Calculating Magnification & Specimen Size
Using millimetres and micrometres as units
● The table below shows how millimetres are related to two other measures of length

37. ● Remember 1mm = 1000µm
● 2000 / 1000 = 2 so the actual thickness of
the leaf is 2mm and the drawing
thickness is 50mm
● Magnification = image size / actual size
= 50 / 2 = 25
● So the magnification is x 25 (NO UNITS)

38. The following diagram may help with unit conversion between
mm and µm: