# Living Things, Cells and Microorganisms

- Link: https://thecuriosi.com/lessons/aptet-evs-living-cells-microorganisms/
- Published: 2026-11-03T18:39:45+05:30
- Author: MAHENDRA MANCHIKALAPATI

1. [Courses](https://thecuriosi.com/courses/)
 2. [APTET EVS Science: Living World and Life Processes](https://thecuriosi.com/courses/aptet-evs-science-living-world-life-processes/)
 3.  Lesson 1 of 8

EVS (Environmental Studies) in Paper I(A) has a Science half and a Social Studies
half. This course covers the science units on the **living world** and **life processes**.
We begin with the most basic questions: what makes something **living**, what living
things are made of (the **cell**), and the tiny living things we cannot see (**microorganisms**).
These ideas are taught informally from Class 3 and come up again in many APTET questions.

## Living and non-living things

**Living things** show these characteristics; **non-living things** do not show 
all of them.

  |  Characteristic |  Example |  
   |  Made of cells |  every plant and animal |  
 |  Need food (nutrition) |  plants make food; animals eat food |  
 |  Respire (release energy from food) |  all living things respire, day and night |  
 |  Grow |  a seedling becomes a tree |  
 |  Respond to stimuli |  touch-me-not (Mimosa) leaves fold when touched; we pull our hand from a hot object |  
 |  Excrete wastes |  urine, sweat; plants give out excess water |  
 |  Reproduce |  seeds, eggs, young ones |  
 |  Move |  animals move from place to place; plants show movement of parts (sunflower, Mimosa) |  
 |  Have a life span and die |  – |

Movement alone does not prove life: a car moves but is non-living. A **seed** looks
lifeless, but it is living: it is **dormant** and grows when it gets water, air 
and warmth.

## The cell: basic unit of life

The **cell** is the basic **structural and functional unit** of life. **Robert Hooke**
first observed cells in 1665, in a thin slice of cork, using a microscope he built.

 * **Unicellular** organisms have one cell that does all functions: amoeba, paramecium,
   bacteria, yeast.
 * **Multicellular** organisms have many cells: plants, animals, humans. Similar
   cells form **tissues**, tissues form **organs**, and organs form **organ systems**.
 * **Prokaryotic** cells have no well-defined nucleus (bacteria); **eukaryotic**
   cells have a nucleus with a nuclear membrane (plants, animals, fungi).

### Parts of a cell and their functions

  |  Part |  Function |  
   |  Cell membrane |  thin outer covering; controls what enters and leaves the cell |  
 |  Cytoplasm |  jelly-like substance in which the other parts lie |  
 |  Nucleus |  controls all activities of the cell; carries hereditary information (chromosomes) |  
 |  Mitochondria |  release energy from food: the **“powerhouse of the cell”** |  
 |  Chloroplasts (plants) |  contain green chlorophyll; make food by photosynthesis |  
 |  Vacuole |  stores water and substances; large in plant cells |  
 |  Cell wall (plants) |  rigid outer layer of cellulose outside the membrane; gives shape and support |

### Plant cell vs animal cell

  |  Plant cell |  Animal cell |  
   |  has a **cell wall** |  no cell wall |  
 |  has **chloroplasts** |  no chloroplasts |  
 |  one large vacuole |  small vacuoles, if any |  
 |  usually regular in shape |  usually irregular or rounded |

Cells differ in shape and size: nerve cells are long (to carry messages), red blood
cells are disc-shaped; the egg of an ostrich is a very large single cell.

## Microorganisms: useful and harmful

**Microorganisms (microbes)** are living things too small to be seen without a microscope.

  |  Group |  Examples |  
   |  Bacteria |  Lactobacillus (curd), Rhizobium (root nodules), bacteria causing typhoid, cholera, tuberculosis |  
 |  Fungi |  yeast, bread mould, mushrooms (large fungi), ringworm fungus |  
 |  Protozoa |  amoeba, paramecium, Plasmodium (malaria) |  
 |  Algae |  Spirogyra, Chlamydomonas |  
 |  Viruses |  cause common cold, measles, chickenpox, polio, dengue, COVID-19; they reproduce only inside the cells of a host |

### Useful microorganisms

 * **Curd:** Lactobacillus bacteria turn milk into curd.
 * **Bread and idli batter:** yeast and other microbes produce carbon dioxide, which
   makes dough rise (fermentation; Louis Pasteur studied fermentation).
 * **Medicines:** antibiotics such as **penicillin**, discovered by **Alexander 
   Fleming** in 1928, come from microorganisms.
 * **Vaccines:** **Edward Jenner** developed the smallpox vaccine (1796); vaccines
   protect against diseases.
 * **Soil fertility:** **Rhizobium** in root nodules of pulses (legumes) **fixes
   nitrogen**; decomposers turn dead matter into manure.

### Harmful microorganisms

 * **Diseases in humans:** malaria (protozoan, spread by the female Anopheles mosquito),
   dengue (virus, spread by the Aedes mosquito), cholera and typhoid (bacteria, 
   spread through contaminated water and food), tuberculosis (bacterium, spread 
   through air).
 * **Diseases in plants and animals:** rust of wheat (fungus), citrus canker (bacterium),
   anthrax in cattle (bacterium).
 * **Food spoilage:** moulds on bread; spoilt milk.

### Exam focus

 * Robert Hooke (cork, 1665); Fleming (penicillin, 1928); Jenner (smallpox vaccine).
 * Cell wall, chloroplasts and a large vacuole: plant cells only.
 * Mitochondria = powerhouse; nucleus = control centre.
 * Malaria is caused by a **protozoan**, not a virus; ringworm is caused by a **
   fungus**, not a worm.
 * Viruses multiply only inside living host cells.

### Example

Mrs Sarala sets up a “living or non-living” sort in Class 3 with real objects: a
seed, a stone, an ant in a jar, a toy car and a potted plant. Children argue about
the seed and the car, then test the seed by sprouting it on wet cotton. The sprout
settles the argument.

## Key takeaways

 * Living things are made of cells, need food, respire, grow, respond, excrete, 
   reproduce and die.
 * The cell is the basic unit of life; Robert Hooke first saw cells in cork.
 * Plant cells have a cell wall, chloroplasts and a large vacuole; animal cells 
   do not.
 * Organisms may be unicellular or multicellular; prokaryotic or eukaryotic.
 * Microbes include bacteria, fungi, protozoa, algae and viruses.
 * Microbes give curd, bread, medicines, vaccines and fertile soil, but also cause
   diseases and spoil food.

## Practice

 1.  Which characteristic is shown by ALL living things?
 2.   * (A) They move from place to place.
      * (B) They respire.
      * (C) They have legs.
      * (D) They make their own food.
 3.  Cells were first observed in a slice of cork by:
 4.   * (A) Louis Pasteur
      * (B) Alexander Fleming
      * (C) Edward Jenner
      * (D) Robert Hooke
 5.  Which structure is found in a plant cell but NOT in an animal cell?
 6.   * (A) cell wall
      * (B) nucleus
      * (C) cell membrane
      * (D) cytoplasm
 7.  The “powerhouse of the cell” is the:
 8.   * (A) nucleus
      * (B) chloroplast
      * (C) mitochondrion
      * (D) vacuole
 9.  The microorganism that turns milk into curd is:
 10.  * (A) yeast
      * (B) Rhizobium
      * (C) Lactobacillus
      * (D) Plasmodium
 11. Malaria is caused by:
 12.  * (A) a protozoan (Plasmodium)
      * (B) a virus
      * (C) a bacterium
      * (D) a fungus
 13. Penicillin was discovered by:
 14.  * (A) Robert Hooke
      * (B) Louis Pasteur
      * (C) Edward Jenner
      * (D) Alexander Fleming
 15. Which of these is a unicellular organism?
 16.  * (A) frog
      * (B) amoeba
      * (C) mango tree
      * (D) earthworm

Answers and explanations (tap to show)

 1. (B) All living things respire; only animals move from place to place, and only 
    green plants make their own food.
 2. (D) Robert Hooke saw cells in cork in 1665.
 3. (A) Only plant cells have a cell wall of cellulose.
 4. (C) Mitochondria release energy from food.
 5. (C) Lactobacillus bacteria change milk into curd.
 6. (A) Malaria is caused by the protozoan Plasmodium, spread by the female Anopheles
    mosquito.
 7. (D) Alexander Fleming discovered penicillin in 1928.
 8. (B) An amoeba is a single cell that carries out all life functions.

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