BIOLOGY REVISION
CHAPTER 1 : CELLS
WHAT IS BIOLOGY?
It is the study of living things.
What are cells?
Cells are the basic units of life. Cells are the simplest part of an organisms that shows all
the 7 characteristics of life MRS RENG.
Movement Reproduction
Respiration Excretion
Sensibility Nutrition
Growth
A microscope is needed to observe the cell as it is microscopic in nature.
THERE ARE 2 TYPES OF CELLS
• Prokaryote
Cells without nucleus e.g: bacterial cell.
• Eukaryote
Cells with nucleus e.g: plant cell, animal cell, fungi, protoctis
ANIMAL CELL :
LIVER CELL :
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BACTERIAL CELL :
PLANT CELL :
FUNCTIONS OF CELL STRUCTURE :
• Cell membrane - forms a barrier between the cell and its surrounding. Controls
movement of other substances into and out of the cell.
• Nucleus - controls all activities in the cell.
• Cytoplasm - place where chemical reactions occur.
• Chloroplast - place where photosynthesis occurs.
• Cell wall - gives shape to cells. Stop cells from bursting when they ll with water.
• Sap vacuole - full of water to maintain shape and rmness of cell.
• Mitochondria - releases energy during aerobic respiration.
• Ribosomes - makes protein for the cell.
DESCRIPTION OF CELL STRUCTURE :
• Cytoplasm - jelly like with particles and organelles in it. It is found enclosed by the cell
membrane.
• Cell membrane - a partially permeable layer that forms a boundary around the
cytoplasm. It is found around the cytoplasm.
• Nucleus - a circular or oval structure containing DNA in the form of chromosomes. It is
found inside the cytoplasm.
• Mitochondria - circular, oval or slipper shaped organelles. It is found inside the
cytoplasm.
• Ribosomes - small, circular structures attached to membranes or lying free. It is found
inside the cytoplasm.
• Cell wall - a tough, non living layer made of cellulose surrounding the cell membrane. It
is found outside the plant cell.
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• Vacuole - a uid lled space surrounding the cell membrane. It is found inside the
cytoplasm of plant cell.
• Chloroplast - an organelle containing chlorophyll. It is found inside the cytoplasm of
some plants.
MICROSCOPE:
There are 2 types of microscope
• Light microscope - uses visible light to observe the specimen.
• Electron microscope - uses a beam of electron to scan the specimen. It gives more
details even if the specimen is at the same magni cation. This means electron has
higher resolution.
MEASUREMENT IN MICROSCOPE :
1cm = 10mm
1mm = 1000 mm (micrometre)
1 mm = 1000 nm (nanometre)
MAGNIFICATION - The number of times the image of a specimen is to its actual size.
THE BACTERIAL CELL :
CIRCULAR DNA - control cell division. Control cell development. Control cell activities.
PLASMIDS - contains genes that carry genetic information to help process survival and
reproduction of the bacterium.
SPECIALISED CELL - it is adapted for a speci c function.
TISSUE - it is a group of cell with similar structures, working together to perform a shared
function.
ORGAN - it is a structure made up of group of tissues, working to gather to perform a
speci c function.
ORGAN SYSTEM - it is a group of organs with related functions, working together to
perform a body function.
Written by SHIVAM CHEEKHOOREE 3
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