BIOLOGY
Chapter 2 (Cells)
AUGUST 23, 2023
Nirjhara
Biology
Chapter-2 (Cells)
Microscopes
-needed to see cells clearly.
-Light microscope are used in school laboratory.
-a very good microscope can magnify about 1500 times.
ELECTRON MICROGRAPH is an image made using microscope.
Cells are the smallest structural and functional unit of life.
Cell Membrane
-every cell has it (plant and animal).
-very thin layer of protein and fat.
-pressed tightly against the inside of the cell wall.
-important layer because it controls what goes in and out of the cell.
-Semi-permeable, only allows entry of water and glucose.
-gives shape to the cell.
-needed for active transport and osmosis.
-provides the transport of micromolecules.
-separates the contents of its cell from the cell’s surroundings.
-doesn’t prevent bursting in highly concentrated solution.
Cell Wall
-all plant cells have it.
-made mainly of cellulose—belongs to a group of
Polysaccharides are carbohydrates
substances called polysaccharides. whose molecules consist of a number
-animal cells don’t have cell walls. of sugar molecules bonded together.
-helps to protect and support the cells.
-Fully permeable, allows the entry of water, minerals and nutrients.
-lignified cell wall gives strength to the plant cell.
Lignified-become rigid and
-prevent bursting in highly concentrated solutions. woody by the deposition of
lignin in cell walls.
Cytoplasm
-a clear jelly of which 70% is water.
-contains many substances dissolved in it. Especially proteins.
-holds other organelles of cell.
-part of the cell where many metabolic reactions take Metabolic reactions-chemical
reactions of life/dynamic changes
place.
of the molecules within a cell.
Vacuole
-fluid-filled space or a sac-like structure inside the cell, containing
mainly water.
-stores food and water. Vesicle-a structure within or outside a
cell, consisting of liquid or cytoplasm
-vacuoles of plants contain solution of sugars and enclosed by a lipid bilayer.
other substances called cell sap.
-vacuoles of animal cells are smaller than those of plants’, contain
solutions and are known as vesicles.
-this large, central vacuole pushes the cytoplasm outwards so that it
forms a thin lining inside the cell wall.
Nucleus (structure containing DNA in the form of chromosomes)
-the genetic information is stored here. genetic information is kept on
the chromosomes which are made of DNA.
-controls all cellular activities such as growth and repair.
-controls what a cell will be. for example, a blood cell or a liver cell etc.
-controls cell division. A cell without nucleus can’t reproduce.
Chloroplasts (small structures found inside some plant cells, inside
which photosynthesis takes place)
-site of photosynthesis.
-organelles that contain the green pigment called chlorophyll.
-they’re found inside the cytoplasm of some plant cells only.
-they absorb light energy from the sun to carry out photosynthesis.
-often contain starch grains made by photosynthesis.
Mitochondria take part in aerobic respiration by using oxygen
and releasing energy from glucose in the form of ATP.
*release energy from glucose and other nutrients by aerobic respiration.*
Ribosomes are very small structures in a cell that use
information on DNA to make protein molecules.
*site of protein synthesis in a cell*
Bacterial Cells (unicellular, do not contain a nucleus)
-have cell walls made of peptidoglycan. we can also say that they’re
made of protein and sugar.
-their cell wall helps to support the cell and prevents it from bursting.
-have a partially-permeable membrane.
-have cytoplasm and ribosomes.
-do not have mitochondria or chloroplast or a nucleus.
-they’re also known as prokaryotic cells—cells with no nucleus.
-have a circle of DNA called bacterial chromosome—provides
instructions for making protein.
-have one or more plasmids—smaller circular molecules of DNA.
*Specialized cells*
Tissues are a group of similar cells that work together to
perform a particular function.
Organs are a group of tissues that work together to perform a
particular function.
Organ system is a system where several organs work together
to perform a particular function.
Magnification means how many times larger an image is than
the actual object.
𝑠𝑖𝑧𝑒 𝑜𝑓 𝑖𝑚𝑎𝑔𝑒
Equation= 𝑠𝑖𝑧𝑒 𝑜𝑓 𝑎𝑐𝑡𝑢𝑎𝑙 𝑜𝑏𝑗𝑒𝑐𝑡
*Sample Question*
1. A cell has been magnified 8 times. The diagram is 40mm wide.
40
Ans: mm=× 5
8
Magnification does not have a unit. Thus, we write × in front of the answer.
*Please go through the book and learn the keywords. This note only contains information, no question
answers. It’s made in such a way that you can answer any question that comes in exam. Ly bitches (no)
-Nir (crying inside.)
