Biology.Useful for grade 9

2. A building is made up of
bricks.
Likewise the bodies of Plants
and animals are made up of
‘cells’

3. Basic components of a cell
Cells are mostly water. The rest of the present
molecules are:
Proteins
Nucleic acid
Carbohydrates
Lipids
others

4. Discovery of Cells

5. 1665-Robert Hooke
 Saw for the first
time cells in a slice
of cork under
microscope.
 Observed them as
‘Honey-comb’
structures and
coined the term
“cell”

6. 1674-Anton van Leeuwenhoek
Discovered
the minute
forms of life
(bacteria).
Single celled
animals in the
drop of water.

7. 1831- Robert
Brown
Discovered
and named
the Nucleus
in a cell.
1839 – J.E.
Purkinje
Used the
term
Protoplasm
for the living
substance in
a cell

8. 1838-Matthias Schlieden
Formulated
cell theory
All plants are
made of cells

9. 1839- Theodor Schwann
Formulated
cell theory
All animals
are made of
cells

10. 1855- Rudolf Virchow
Cells can only
arise from
pre-existing
cells

11. Observation of cells under Microscope
Plasma
Membrane
Nucleus
Cytoplasm
Cheek Cells Stained with Methylene Blue

12. Unicellular organism vs. Multicellular
organism

13. Unicellular Multicellular
• Represented by a single
cell.
•Consists of large number
of cells.
• Activities are performed
by a single cell.
•Single cell performs one or
few activities.
• No division of labour. •Cells are specialised to
perform different functions
so that there is division of
labour.
• Reproduction by the
single cell.
•Germ cells take part in
reproduction, others
remain intact.
• Eg: Amoeba, Euglena,
Bacteria, Mycoplasma,etc.,
• Eg: Fungi, plants,
animals.

14. Size and shape of the cell
 Size and Shape depend upon its function.
 Red blood cells are small and disc shaped to fit
through the smallest blood vessel.
 Muscle cells are long and thin. When they contract
they produce movement.
 Nerve cells which carry signals to the brain are very
long.

15. Size and shape of the cell
 Smallest Cell – Mycoplasma (0.1-0.5 μm)
 Largest Cell – Ostrich Egg (18cm)
 Longest Animal Cell – Nerve Cell (90-100 cm)
In elephant - Nerve Cell (3 m)

16. Compound Microscope Transmission Electron
Microscope

17. Scanning electron microscope

18. Differences between Prokaryotic
and Eukaryotic cell
Prokaryotic cell Eukaryotic cell
• Small in size (1 – 10 μm) • Larger in size (5 – 100 μm)
• Nuclear membrane is absent. It is
called nucleoid
• Nuclear membrane is present
• A single DNA / chromosome molecule
is present
• Two or several DNA / chromosome
molecules are present
• Nucleolus is absent • Nucleolus is present
• Membrane bound organelles are
absent
• Membrane bound organelles are
present
• Vacuoles are absent • Vacuoles are present

20. Prokaryotic cell

22. Bacteria be like!!!

26. Structure and Organisation of the
Cell
 Plasma membrane, Nucleus and Cytoplasm - common
to all cells – functional region of the cell

27. Plasma membrane
Structure
 Outermost, delicate, elastic and selectively permeable
membrane
 Separates the contents from the external environment
 Living cells made up of lipids
 Proteins are located inside and outside the membrane
 Carbohydrates are attached at places to outer surface of
proteins and lipids

28. Plasma membrane
Functions
 Provides a definite shape to the semi-fluid contents of the
cell
 Functions as a mechanical barrier that protects the inner
contents
 Due to selective permeability, the membrane determines
the substances to be allowed to enter or exit
 The flexibility of the membrane enables the cell to engulf
food and other substances from its external environment –
ENDOCYTOSIS – Eg. Amoeba

29. Plasma membrane
Functions
 It has chemicals which help in tissue formation,
distinguishing foreign substances and defense against
microbes
 It provides flow of information amongst different cells
of the same organism

30. Transport across the membrane
 Membranes access physical barriers between the
organelles of a cell and the cytoplasm and between the
cell and its surrounding environment
 Types of membranes:
 Impermeable – Substances do not pass through
 Permeable – Both solute and solvent pass through
 Semi-permeable – Only solvent passes through
 Selectively permeable – Allows solvent and some selected
solutes

31. Transport across the membrane
 Types of transport:
 Passive transport – Passage of substances across the
plasma membrane without expenditure of energy
 Active transport – Requires the use of energy – Proteins,
Amino acids, etc.

32. Types of Passive Transport
 Osmosis – Movement of water or solvent across the
semi-permeable membrane from a region of higher
concentration to a region of lower concentration
 Diffusion – The process of movement of solute
(solid, liquid, gas) from a region of higher
concentration to a region of lower concentration to
spread uniformly in the given space. Eg. Room
spray, CuSO4 crystals

33. Importance of Osmosis
 Absorption of water by roots
 Movement of water from cell to cell
 Turgidity or stretched form of the cell
 Movement of plants due to loss or gain of water
 Opening and closing of stomata
are all due to Osmosis.
Osmosis occurs only in living cells.

34. Importance of Diffusion
 Different substances spread throughout the
cytoplasm without much delay
 Osmosis is a type of diffusion where only solvent is
allowed to diffuse
 The exchange of respiratory gases between the cells
and the environment is due to diffusion
 Transpiration in plants is due to diffusion
 Aroma of the flowers is due to diffusion, which
attracts insects and animals for pollination

35. Differences between Osmosis
and Diffusion
Osmosis Diffusion
• Movement of solvent from
the region of higher
concentration to the region
of lower concentration
• Movement of solute from a
region of higher
concentration to a region of
lower concentration
• Takes place only in the
liquid medium
• Takes place in solid, liquid
and gaseous medium
• Requires semi-permeable
membrane
• Does not require a semi-
permeable membrane
• Does not equalize the
concentration of the solvent
on both sides of the
membrane
• Equalizes the
concentration of the solute
throughout the available
space

36. Types of Osmotic Solutions
1. Hypotonic solution –
Concentration of the solvent on the external medium of
the cell is higher than that in the internal medium of the
cell. As a result, solvent (water) moves from the external
medium into the internal medium of the cell. As plasma
membrane is semi-permeable, water will move across
both directions. However, more water will enter the cell
and the cell will swell – ENDOSMOSIS
Excessive endosmosis – (a) Bursts animal cell (b) Does
not burst plant cell due to cell wall

37. Hypotonic Solution
Solvent (high
concentration)

38. Types of Osmotic Solutions
2. Isotonic solution –
Concentration of the solvent on the external medium
of the cell and in the internal medium of the cell are
same. As a result, the solvent (water) going in and
out of the cell is the same. Therefore, no movement
of water . The cell size remains the same.

39. Isotonic Solution
Solvent

40. 3. Hypertonic Solution -
Concentration of the solvent on the external medium
of the cell is lower than that in the internal medium
of the cell. As a result, solvent (water) moves from
the internal medium of the cell into the external
medium. As plasma membrane is semi-permeable,
water will move across both directions. However,
more water will pass out of the cell and the cell will
shrink – EXOSMOSIS
Contraction of the protoplasm away from the cell
wall is called PLASMOLYSIS.
Types of Osmotic Solutions

41. Hypertonic Solution
Solute (higher
concentration)

42. Cell Wall
Structure
 Found in plants, fungi and prokaryots
 Rigid, semi-elastic, semi-transparent
 Protective covering, present outside the cell membrane
 Made up of cellulose (cannot be digested by humans)
 Complex fibrous carbohydrate
 Gives structural strength to the cell
 Cell wall possesses many small pores through which
adjacent cells are connected with cytoplasmic bridges
– plasmodesmata

43. Cell Wall
Functions
 Provides shape and strength to the cells of the plant
 Protects the cells against pathogens and mechanical injury
 Prevents bursting of cell on endosmosis - as water enters
living cells, protoplasm swells up and exerts pressure
against the cell wall. The cell wall exerts an equal and
opposite pressure against the swelling protoplasm. As a
result, further entry of water is stopped.
 Protects the plant cell from various environmental
conditions

44. Nucleus
Structure
 Dense protoplasmic body
 Contains hereditary information for controlling cell activities and for
transfer of information to the next generation
 Largest cell structure
 Oval or spherical in shape
 Has double membrane – nuclear membrane
 Lies in the centre of the cell – animal and young plant cell
 In mature plant cell, lies in the periphery due to large vacuole
 In prokaryotic cells (eg. Bacteria), the nuclear membrane is absent. It
remains as nucleic acid, which is called nucleoid.
 RBC in mammals lacks nucleus at maturity
 Sieve elements in plants lacks nuclei
 Cells without nucleus cannot survive
 Most of the cells have one nucleus. More than one nucleus in some
organisms like paramecium (2 nuclei)

45.  Has double membrane – nuclear membrane – (a)
separates nucleus from cytoplasm (b) it has pores to
allow exchange of materials between nucleus and
cytoplasm
 Nucleoplasm – colourless, dense sap with chromatin
thread and nucleolus suspended in it
 Nucleolus – (a) one or more round structure found
inside the nucleus (b) Rich in RNA and protein (c) No
membrane (d) Site of ribosome formation
Parts of the Nucleus

46. Parts of the Nucleus
 RNA helps in protein synthesis
 Chromatin thread is made up of DNA and protein. During cell
division, chromatin becomes highly condensed, thick rod like
structures – CHROMOSOME
 Number of chromosomes are fixed for a species – humans: 23
pairs
 Chromosomes carry and help in transfer of information for
inheritance of characters from parents to the next generation
 DNA contains genetic information
 Segments of DNA function as genes
 Genes are arranged in a linear fashion over DNA or
chromosomes
 Genes contain all the information for functioning, growth and
reproduction of the cell and also of the whole organism

47. Functions of the Nucleus
 Contains all genetic information, not only for the cell,
but for the whole organism
 Functions as control centre of the cell, as it controls
the cell metabolism and cell activities
 Ribosomes are formed by nucleolus, which is part of
the nucleus
 By the effect of environment and selective functioning
of genes, nucleus brings about cell differentiation, by
which cell attains specific structure and function
 Division of nucleus is essential for cell division

48. Cytoplasm
 The protoplasmic mass, excluding the nucleus, is cytoplasm
 In young cell, cytoplasm completely fills the space between the
nucleus and plasma membrane
 As the cell increases in size, small cavities of vacuoles appear
 It is viscous, homogenous, colloidal liquid
 Contains various molecules such as water, amino acids,
carbohydrates, lipids, proteins, etc.
 Also contains various organelles and non-living substances like
cell inclusions
 In eukaryotic cell, the organelles are membrane bound
 Viruses lack any membrane so do not show any characteristic of
life. They do not have any metabolic machinery of their own.
They utilise the metabolic machinery of the living cell and
multiply

49. Cell Organelles
 Structures which have characteristic form and
function
 They are same throughout the living world
 They continue to survive and perform their function
even outside, if provided with environmental
condition similar to cytoplasm
 Double membrane – mitochondria, plastids
 Single membrane – ER, Golgi apparatus, lysosome,
vacuoles
 Membraneless - ribosomes

50. Endoplasmic Reticulum
 Complex network of membrane bound channels, sheets
 They looks like tubules and vesicles
 Continuous between nuclear membrane and plasma
membrane
 The membranes are similar in structure to the plasma
membrane
 ER – Present in all cells except prokaryots and mammalian
RBC
 Types of ER
 Rough Endoplasmic Reticulum – RER – Characterised by the
presence of ribosomes on its surface
 Smooth Endoplasmic Reticulum – SER – Devoid of ribosomes
on its surface

51. Endoplasmic Reticulum
 Functions
 RER is a site of protein synthesis
 SER helps in lipids and steroids synthesis
 Proteins and lipids synthesised in ER is used for building cell
membrane and the process is called MEMBRANE BIOGENESIS
 Proteins function as enzymes. Proteins and lipids form hormones
 ER helps in inter-cellular and intra-cellular transport of substances
 It gives internal support to the cytoplasm
 It provides large surface area for the synthesis of many chemicals
and various physiological activities
 SER in liver cells takes part in detoxifying many poisons and drugs
 Differences
RER SER
• Ribosomes are present • Ribosomes are absent
• Specialised to synthesise
proteins
• Specialised to synthesise
lipids and steroids

52. Golgi Apparatus
 Discovered by Camillo Golgi
 Membrane bound sacks, tubules and vesicles
 Specialised to elaborate and secrete complex biochemicals
 Lies near the nucleus
 Found in all eukaryotic cells except mammalian RBC
 The membrane bound sacks of golgi apparatus are thin and
curved and are called CISTERNAE
 Cisternae occur in small stacks
 Membranes of golgi apparatus may develop connections with
membranes of ER to form complex cellular membrane system
 The materials synthesised near ER are packaged and dispatched
to inter-cellular and intra-cellular targets

53.  Functions
 Involved in repair and synthesis of cell membrane
 Lysosomes are formed by golgi apparatus
 Secretion is the major function. All types of substances,
which are to be secreted or excreted, are packed in vesicles by
golgi apparatus for passage through the outside
 It takes part in storage, modification and packaging of various
biochemicals produced by different components of the cell
 Components of cell wall are synthesised by golgi apparatus in
plants
 Complex and special sugars (galactose) are made by golgi
apparatus
Golgi Apparatus

54. ER and Golgi Apparatus

55. Lysosome
 Small spherical vesicles covered by single membrane
 Found in all animal cells, except mammalian RBCs and
plant cell
 Contains digestive enzymes for intra-cellular digestion and
waste disposal. Due to this, they are called DIGESTIVE
BAGS
 Digestive enzymes are synthesised by RER
 The enzymes are released only when the cell has been
damaged
 Old organelles, germs, food, etc. enter the lysosomes for
disposal by digestion
 In damaged cell, lysosomes digest cellular components and
they will burst. So, they are called SUICIDE BAGS

56.  Functions
 Helps in destruction of foreign particles (bacteria and
viruses). So, they provide protection to the body.
 Help in intra-cellular digestion of food particles
 Help in removing dead and worn-out cellular organelles
by digesting them
Lysosome

57. MITOCHONDRIA

58. Mitochondria
 Structure
 Rod shaped or sausage shaped organelle
 Commonly known as power house of the cell because
they contain enzymes for total oxidation of food and
for release of high amount of energy in the form of
Adenosine Tri Phosphate (ATP) molecules
 ATP is the energy currency of the cell
 The body uses energy stored in ATP for synthesis of
new chemical compounds and for mechanical work

59. Mitochondria
 The Mitochondria structure has three main parts:
 Each mitochondrion is bounded by two membranes
 OUTER MEMBRANE: covers the mitochondria.
It is smooth and porous
 INNER MEMBRANE:
 Inner membrane is folded inwards to form CRISTAE
 Cristae increases the surface area for ATP generating chemical reactions
 So…the more space it has the more energy it can create
 MATRIX: a fluid that has water and proteins , having DNA, ribosomes and enzymes all mixed
together (like a solution)
 The proteins take the food molecules in and combine them with Oxygen to release the energy
 DNA and ribosomes make the mitochondria semi-autonomous because they manufacture their
own proteins and enzymes
 Enzymes take part in respiration
•

60. Mitochondria
 Functions
 It is a site where aerobic respiration is performed
 It provides energy in the form of ATP for vital activities
of living cells, like synthesis of chemical compounds,
their transport and for mechanical work
 They make some of their own protein

61. Plastids
 Large organelles found only in plant cell
 It is a site of synthesis and storage of organic substances
 Types of plastids - There are two types on the basis of pigments
present
 Leucoplast
1. It is a colourless plastid
2. Stores food in the plant body as starch protein and fat
3. It is mostly present in storage cells, such as roots, underground stems, etc.
 Chromoplast
It is a coloured plastid
(a) non-green coloured includes red, orange, yellow, etc. present in fruits and
flowers
(b) green chloroplast
- kitchen of the cell abundant in green leaves and also in green parts of
the shoot.
- They trap solar energy and synthesise food by the process of
photosynthesis.
- Chloroplast is bounded by two membranes
- The inside of the chloroplast is clearly marked into colourless ground
matrix called stroma. This contains enzymes for dark reactions of
photosynthesis
 Like mitochondria, plastids contain their own DNA and ribosomes
for their own protein synthesis

62. Plastids
 Functions
 Chromoplast provides colour to fruits and flowers,
which helps in pollination and seed dispersal
 Leucoplasts help in storage of proteins, starch and lipids
 Chloroplasts trap solar energy to manufacture food
through photosynthesis
 Chloroplasts balance oxygen and carbon dioxide
through photosynthesis

63. Ribosomes
 Extremely small, rounded bodies
 Found either in free state in cytoplasm or attached to
the surface of ER
 Composed of RNA and proteins
 Membraneless
 Present in eukaryotes and prokaryotes
 Absent in mammalian RBCs
 Function – It is a site of protein synthesis

64. Vacuoles
 They are storage sacks
 Contains non-living, solid or liquid contents (food)
 Vacuoles are small in animal cell, very large in plant cell
 Sap vacuole
 Fluid content of the vacuole is called cell sap
 In mature plant cell, central vacuole occupies 50-90% of the cell
volume
 Cell sap provides turgidity and rigidity to the cell
 Cell sap stores salts, sugars, amino acids, organic acids and some
proteins
 Cell sap is also a dump for waste products
 Food vacuole
 In a single cell organism, like amoeba, the vacuole is called food
vacuole
 The sacks containing ingested food particles fuse with lysosomes to
form food vacuoles
 Digestion occurs inside the food vacuole

65. Vacuoles
 Contractile vacuole
 In some unicellular organisms, there are specialised
vacuoles called contractile vacuoles
 They expel excess water and some wastes from the cell
 Functions of vacuoles
 They play an important role in expelling excess water
and some wastes from the cell in some unicellular
organisms
 They store metabolic bi-products or end products of
plant cell
 They provide turgidity and rigidity to the cell