Unit 18: Organisation of Life - NMMS - 8th Std
Here is a comprehensive study note guide for Unit 18: Organisation of Life, specifically designed for NMMS and TNPSC exam preparation. These notes cover all classifications, specific measurements, scientific terms, and physiological processes mentioned in the text without missing key details.
Unit 18: Organisation of Life
1. Biological Organisation & Classification
Hierarchy of Life: Biological organization starts from the submicroscopic molecular level and moves to the macroscopic organismic level.
Sequence: Atoms → Molecules → Organelles → Cells → Tissues → Organs → Organ Systems → Organism.
Classification based on Cell Structure:
Prokaryotes: Organisms where a true nucleus is absent (e.g., Bacteria, Cyanobacteria, Mycoplasma).
Eukaryotes: Organisms with a well-defined nucleus covered by a membrane (e.g., Plants, Animals).
Classification based on Cell Number:
Unicellular: Single-cell body (e.g., Yeast, Amoeba).
Multicellular: Made of large numbers of cells (e.g., Plants, Animals, Humans).
2. The Cell (Structural Unit)
Definition: The cell is the structural and functional unit of life, known as the "building blocks of life".
Study: The study of cells is called Cell Biology.
Development: Our body develops from a single cell called a Zygote. The process by which fetal cells attain changes in structure and function is called Cell Differentiation.
Measurement: Cell size is measured in microns ($\mu m$). One micron is $1/1,000,000$ meter.
Important Exam Data (Cell Sizes):
Average cell size: 0.5 to 20 $\mu m$.
Smallest cell (General): Bacteria ($1-2~\mu m$).
Smallest bacterium: Mycoplasma (0.0001 mm diameter).
Smallest human cell: Red Blood Cells (RBC) - 7 $\mu m$ diameter.
Longest human cell: Nerve cell - 90 to 100 cm length.
Human Egg (Ovum): 100 $\mu m$.
Largest cell: Egg of an Ostrich.
3. Tissues
Definition: Groups of cells with similar structure performing a specific function.
Types of Tissues based on Composition:
Simple Tissue: Homogeneous (made of cells of the same type). E.g., Glandular tissue.
Complex Tissue: Heterogeneous (made of different kinds of tissues). E.g., Dry skin tissue.
Four Basic Animal Tissues:
Epithelial: Covering tissue for protection.
Muscular: Contractile tissue for movements and locomotion.
Connective: Supporting tissue for binding different body structures.
Nervous: Tissue for conduction of nerve impulses.
4. Organs: The Eye
The eye is a photoreceptor organ compared to a camera. It can differentiate approximately 10-12 million colors.
A. External Structure (Visible Parts)
Sclera: "White of the eye." Tough, thick white sheath that protects inner parts.
Conjunctiva: Thin transparent membrane spread across the sclera. It keeps eyes moist by secreting mucus and tears.
Cornea: Transparent layer over the pupil and iris. Main role is to refract light.
Iris: Pigmented (colored) layer. Controls the size of the pupil based on the amount of light entering.
Pupil: Small opening in the middle of the iris that allows light to enter.
B. Internal Structure
Lens: Transparent, biconvex, made of protein. It acts with the cornea to refract light and focus it on the retina.
Retina: Layer at the back where images are formed. It converts light into impulses.
Optic Nerve: Located behind the retina. It carries nerve impulses to the brain.
Aqueous Humour: Watery fluid between the lens and cornea. It nourishes both the lens and cornea.
Vitreous Humour: Semi-solid, transparent, jelly-like substance inside the eye. It maintains the shape of the eye.
5. Organ Systems: The Respiratory System
Pathway of Air: Nostrils → Nasal Cavity → Pharynx → Larynx → Trachea → Bronchi → Bronchioles → Alveoli.
Nose: Inner surface is lined with cilia and mucous cells to trap dust/germs. Blood vessels here warm the inhaled air.
Larynx: Known as the Voice Box. Contains tissue folds that vibrate to produce sound.
Trachea: Also called the Windpipe. It is an elastic tube.
Lungs: Spongy elastic bags in the thoracic cavity. The left lung is slightly smaller than the right to accommodate the heart.
Alveoli: Tiny air sacs at the end of bronchioles where exchange of Oxygen and Carbon dioxide takes place.
Breathing Mechanism:
Breathing Rate: 15–18 times/minute at rest; up to 25 times/minute during heavy exercise.
Inhalation (Inspiration):
Diaphragm muscles contract and move downward.
Ribs move upwards and outwards.
Thoracic volume increases, pressure decreases → Air flows IN.
Exhalation (Expiration):
Diaphragm muscles relax and move upward.
Ribs move downwards.
Thoracic volume decreases, pressure increases → Air flows OUT.
6. Physiological Processes
A. Homeostasis
Definition: Self-regulating process to maintain a stable internal environment (balance) for survival.
Examples:
Thermoregulation: Mammals are warm-blooded (maintain constant body temperature). Sweat reduces temperature; shivering raises temperature.
Glucose Control: Insulin hormone is secreted when blood glucose rises; Glucagon hormone is secreted when it falls.
B. Diffusion
Definition: Movement of particles from an area of higher concentration to lower concentration to equalize concentration.
Key Point: Can occur without a membrane. Occurs in liquids and gases.
Examples: Perfume spreading in a room, ink drop in water, tea powder in hot water, exchange of respiratory gases in alveoli/tissues.
C. Osmosis
Definition: Movement of solvent (water) particles across a semi-permeable membrane from a dilute solution (more water) to a concentrated solution (less water).
Types of Solutions:
Isotonic: Concentration is the same inside and outside the cell.
Hypotonic: External solution is dilute (less concentrated). Water rushes INTO the organism (Cells swell).
Hypertonic: External solution is concentrated. Water rushes OUT of the organism (Cells shrink).
D. Osmoregulation
Definition: Regulating water balance and electrolytic concentration to maintain homeostasis.
Term Coined by: Hober in 1902.
Types:
Osmoconformers: Body matches surrounding osmolality (e.g., Marine invertebrates).
Osmoregulators: Maintain internal osmolality different from the environment.
Freshwater Fish: Do not drink water; produce large amounts of dilute urine; absorb salt via gills.
Marine Fish: Drink seawater; excrete salt via gills; produce very little urine to conserve fluids.
E. Cellular Respiration
Definition: Breaking down glucose to release energy in the form of ATP. It occurs in the Cytoplasm and Mitochondria.
Aerobic Respiration:
Takes place in the presence of Oxygen.
Equation: Glucose + Oxygen → Carbon dioxide + Water + Energy.
Energy: Releases 19 times more energy than anaerobic (36 ATPs per glucose molecule).
Anaerobic Respiration:
Takes place in the absence of Oxygen (e.g., Yeast, human muscle cells).
Products: Ethyl alcohol (Ethanol) or Lactic acid + $CO_{2}$ + Very little Energy.
F. Metabolism
Definition: Sum of chemical reactions to sustain life.
Basal Metabolism: Minimum energy required to maintain normal activities during complete rest (measured 12-18 hours after food intake).
Types:
Anabolism (Constructive): Building and storing. Small molecules → Complex molecules.
Examples: Amino acids → Enzymes/Proteins; Glucose → Glycogen.
Catabolism (Destructive): Breaking down to release energy.
Examples: Carbohydrates → Glucose; Glucose → $CO_{2}$ + Water + Heat.
Here are the 50 multiple-choice questions (MCQs) based on the "Organisation of Life" unit, with the citation tags removed as requested.
Topic: Biological Organisation & Cells
1. Biological organisation starts with which level?
a) Cellular level
b) Organismic level
c) Submicroscopic molecular level
d) Microscopic level
Answer: c) Submicroscopic molecular level
2. Organisms that lack a true nucleus are called:
a) Eukaryotes
b) Prokaryotes
c) Multicellular
d) Vertebrates
Answer: b) Prokaryotes
3. Which of the following is a unicellular organism?
a) Human
b) Plant
c) Yeast
d) Fish
Answer: c) Yeast
4. Our body is developed from a single cell called:
a) Embryo
b) Fetus
c) Zygote
d) Neuron
Answer: c) Zygote
5. One micron is equal to:
a) 1/100 meter
b) 1/1000 meter
c) 1/100000 meter
d) 1/1000000 meter
Answer: d) 1/1000000 meter
6. The smallest bacterium is:
a) E. coli
b) Mycoplasma
c) Salmonella
d) Lactobacillus
Answer: b) Mycoplasma
7. What is the diameter of a Red Blood Cell (RBC)?
a) 7 µm
b) 100 µm
c) 1-2 µm
d) 20 µm
Answer: a) 7 µm
8. The longest cell in the human body is:
a) Muscle cell
b) Bone cell
c) Nerve cell
d) Epithelial cell
Answer: c) Nerve cell
9. Which is the largest cell among multicellular animals?
a) Human egg
b) Nerve cell
c) Egg of an Ostrich
d) Sperm cell
Answer: c) Egg of an Ostrich
10. The process by which fetal cells change structure and function is known as:
a) Cell division
b) Cell differentiation
c) Metabolism
d) Osmosis
Answer: b) Cell differentiation
Topic: Tissues & Organs
11. Which type of tissue is responsible for movements and locomotion?
a) Epithelial tissue
b) Connective tissue
c) Muscular tissue
d) Nervous tissue
Answer: c) Muscular tissue
12. Simple tissues are:
a) Heterogeneous
b) Homogeneous
c) Complex
d) Made of different types of cells
Answer: b) Homogeneous
13. Which tissue conducts nerve impulses?
a) Epithelial
b) Nervous
c) Connective
d) Muscular
Answer: b) Nervous
14. The human eye can be compared to a:
a) Microscope
b) Camera
c) Telescope
d) Periscope
Answer: b) Camera
15. Approximately how many colors can the human eye differentiate?
a) 1-2 million
b) 5-6 million
c) 10-12 million
d) 20-25 million
Answer: c) 10-12 million
16. The tough, thick white sheath of the eye is called:
a) Cornea
b) Iris
c) Sclera
d) Pupil
Answer: c) Sclera
17. Which part of the eye refracts light?
a) Iris
b) Sclera
c) Cornea
d) Retina
Answer: c) Cornea
18. The colored portion of the eye that controls pupil size is:
a) Cornea
b) Iris
c) Lens
d) Retina
Answer: b) Iris
19. Which part carries nerve impulses from the retina to the brain?
a) Cornea
b) Lens
c) Optic nerve
d) Pupil
Answer: c) Optic nerve
20. The watery fluid between the lens and cornea is:
a) Vitreous Humour
b) Aqueous Humour
c) Tears
d) Plasma
Answer: b) Aqueous Humour
Topic: Respiratory System
21. The voice box is also known as:
a) Pharynx
b) Trachea
c) Larynx
d) Bronchus
Answer: c) Larynx
22. The windpipe is scientifically called:
a) Oesophagus
b) Trachea
c) Larynx
d) Pharynx
Answer: b) Trachea
23. Which lung is slightly smaller to allow room for the heart?
a) Right lung
b) Left lung
c) Both are same size
d) None
Answer: b) Left lung
24. Exchange of gases takes place in tiny air sacs called:
a) Bronchi
b) Trachea
c) Alveoli
d) Pharynx
Answer: c) Alveoli
25. During heavy exercise, the breathing rate can increase up to:
a) 15 times/minute
b) 18 times/minute
c) 25 times/minute
d) 50 times/minute
Answer: c) 25 times/minute
26. During inhalation, the diaphragm moves:
a) Upward
b) Downward
c) Sideways
d) Does not move
Answer: b) Downward
27. During exhalation, the volume of the thoracic cavity:
a) Increases
b) Decreases
c) Remains same
d) Doubles
Answer: b) Decreases
Topic: Physiological Processes (Homeostasis, Diffusion, Osmosis)
28. The maintenance of a stable internal environment is called:
a) Metabolism
b) Homeostasis
c) Osmosis
d) Diffusion
Answer: b) Homeostasis
29. Which hormones control blood glucose level?
a) Adrenaline and Thyroxine
b) Insulin and Glucagon
c) Estrogen and Progesterone
d) Growth hormone
Answer: b) Insulin and Glucagon
30. Movement of particles from higher to lower concentration is called:
a) Osmosis
b) Active transport
c) Diffusion
d) Digestion
Answer: c) Diffusion
31. The spread of perfume smell in a room is an example of:
a) Osmosis
b) Diffusion
c) Respiration
d) Circulation
Answer: b) Diffusion
32. Osmosis involves the movement of solvent across a:
a) Permeable membrane
b) Semi-permeable membrane
c) Cell wall
d) Nuclear membrane
Answer: b) Semi-permeable membrane
33. In a hypotonic solution, water moves:
a) Into the cell
b) Out of the cell
c) No movement
d) Equal movement both ways
Answer: a) Into the cell
34. If a cell shrinks, the external solution is:
a) Isotonic
b) Hypotonic
c) Hypertonic
d) Neutral
Answer: c) Hypertonic
35. The term Osmoregulation was coined by:
a) Robert Hooke
b) Hober
c) Fleming
d) Pasteur
Answer: b) Hober
36. Marine organisms are mostly:
a) Osmoregulators
b) Osmoconformers
c) Thermoregulators
d) None of the above
Answer: b) Osmoconformers
37. Freshwater fish produce:
a) Small amount of concentrated urine
b) Large amount of dilute urine
c) No urine
d) Large amount of concentrated urine
Answer: b) Large amount of dilute urine
38. Marine fish excrete salt through:
a) Kidneys
b) Skin
c) Gills
d) Liver
Answer: c) Gills
Topic: Respiration & Metabolism
39. Cellular respiration releases energy in the form of:
a) DNA
b) RNA
c) ATP
d) ADP
Answer: c) ATP
40. Aerobic respiration requires:
a) Nitrogen
b) Carbon dioxide
c) Oxygen
d) Hydrogen
Answer: c) Oxygen
41. How many ATPs are produced per glucose molecule in aerobic respiration?
a) 2
b) 19
c) 36
d) 38
Answer: c) 36
42. Anaerobic respiration in yeast produces:
a) Water
b) Ethyl alcohol (Ethanol)
c) Oxygen
d) Glucose
Answer: b) Ethyl alcohol (Ethanol)
43. Aerobic respiration releases how many times more energy than anaerobic?
a) 10 times
b) 19 times
c) 25 times
d) 36 times
Answer: b) 19 times
44. Metabolism consists of:
a) Digestion and excretion
b) Breathing and circulation
c) Anabolism and Catabolism
d) Growth and repair
Answer: c) Anabolism and Catabolism
45. Constructive metabolism is called:
a) Catabolism
b) Anabolism
c) Digestion
d) Respiration
Answer: b) Anabolism
46. Breakdown of glucose into CO2 and water is an example of:
a) Anabolism
b) Catabolism
c) Photosynthesis
d) Absorption
Answer: b) Catabolism
47. Amino acids building into proteins is an example of:
a) Catabolism
b) Anabolism
c) Excretion
d) Diffusion
Answer: b) Anabolism
48. Basal metabolism is measured after how many hours of food intake?
a) 2-4 hours
b) 6-8 hours
c) 12-18 hours
d) 24 hours
Answer: c) 12-18 hours
49. Mammals are:
a) Cold-blooded
b) Warm-blooded
c) Osmoconformers
d) Invertebrates
Answer: b) Warm-blooded
50. During shivering, the body:
a) Lowers temperature
b) Produces heat
c) Sweats
d) Sleeps
Answer: b) Produces heat
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