Paper IPaper I · General Science
Cell and Classification of Life
Cell theory and organelles, prokaryotic versus eukaryotic cells, plant versus animal cells, tissues, the five-kingdom classification, binomial nomenclature, and basic genetics vocabulary, with discoverers, years and applications at CAPF recognition depth
CAPF wiki•9 min read•21 sections
At a glance
PaperPaper ISubjectGeneral ScienceSyllabusGeneral Science: general awareness, scientific temper, comprehension and appreciation of scientific phenomena of everyday observation, including new areas such as Information Technology, Biotechnology, and Environmental ScienceImportanceHigh
BiologyCellCell TheoryOrganellesProkaryoteEukaryoteClassificationFive Kingdoms
This note covers the organising units of biology: the cell and its organelles, how plant and animal cells differ, how living things are sorted into kingdoms, and the vocabulary of genetics. CAPF tests the "powerhouse of the cell" type fact (the mitochondrion), the organelle-to-function match, which features are unique to plant cells, the names of the five kingdoms and their proposer, the father-of titles (Mendel, Linnaeus, Hooke), and basic terms such as gene, chromosome and DNA. The depth target is NCERT Class VIII to X. These are pure recognition facts, so a well-built reference table here converts directly into marks.
- The cell is the basic structural and functional unit of life. It was first observed and named by Robert Hooke (1665) while examining cork through a microscope; he saw box-like compartments and called them "cells".
- Anton van Leeuwenhoek first saw living cells (microbes) under a microscope. Robert Brown discovered the nucleus (1831).
- The cell theory (Matthias Schleiden and Theodor Schwann, 1838 to 1839; extended by Rudolf Virchow) states that all living things are made of cells, the cell is the basic unit of life, and every new cell arises from a pre-existing cell.
- Cells differ in size and shape: the ostrich egg is the largest single cell; nerve cells are the longest; bacteria are among the smallest.
- A prokaryotic cell (bacteria, cyanobacteria) has no true membrane-bound nucleus and no membrane-bound organelles; its genetic material lies free in the cytoplasm.
- A eukaryotic cell (plants, animals, fungi, protists) has a true membrane-bound nucleus and membrane-bound organelles.
- Cell membrane (plasma membrane): the selectively permeable outer boundary that controls the entry and exit of substances; present in all cells.
- Cell wall: a rigid outer layer of cellulose, present in plant cells (in fungi it is chitin, in bacteria it is peptidoglycan); gives shape and protection. Absent in animal cells.
- Nucleus: the control centre, holds the genetic material (DNA on chromosomes); discovered by Robert Brown.
- Mitochondrion: the powerhouse of the cell, the site of aerobic respiration and energy (ATP) production; has its own DNA.
- Ribosome: the site of protein synthesis; the smallest organelle, found free or on the endoplasmic reticulum.
- Endoplasmic reticulum (ER): the transport network; rough ER (with ribosomes) makes proteins, smooth ER makes lipids.
- Golgi apparatus (Golgi body): packaging, modification and dispatch of materials.
- Lysosome: the suicide bag of the cell; contains digestive enzymes that break down waste and worn-out parts; found mainly in animal cells.
- Vacuole: storage of water, food and waste; large and central in plant cells, small or absent in animal cells.
- Chloroplast: contains the green pigment chlorophyll, the site of photosynthesis; present only in plant cells.
- Plastids (in plants): chloroplasts (green, photosynthesis), chromoplasts (coloured pigments), leucoplasts (storage).
| Feature |
Plant cell |
Animal cell |
| Cell wall |
Present (cellulose) |
Absent |
| Chloroplast and plastids |
Present |
Absent |
| Vacuole |
Large, central |
Small or absent |
| Centriole |
Usually absent |
Present |
| Shape |
Usually fixed, rectangular |
Usually rounded, irregular |
| Lysosome |
Rare |
Common |
- A tissue is a group of similar cells doing a common function. Plant tissues include meristematic (dividing) and permanent tissues; animal tissues are epithelial (covering), connective (blood, bone), muscular and nervous.
- Tissues form organs, organs form organ systems, and systems form the organism. This hierarchy links directly to human body and systems.
- Monera: prokaryotes, single-celled, no true nucleus (bacteria, cyanobacteria).
- Protista: single-celled eukaryotes (amoeba, paramoecium, euglena, plasmodium).
- Fungi: heterotrophic, mostly saprophytic, cell wall of chitin (mushrooms, yeast, moulds, Penicillium).
- Plantae: multicellular, autotrophic, make their own food by photosynthesis, cell wall of cellulose.
- Animalia: multicellular, heterotrophic, no cell wall, mostly mobile.
- Carolus Linnaeus is the father of taxonomy; he gave the binomial nomenclature system, a two-part Latin name of genus and species (for example Homo sapiens for humans, Panthera tigris for the tiger). The genus name is capitalised, the species name is not, and both are italicised or underlined.
- The classification hierarchy from broad to narrow: Kingdom, Phylum (or Division in plants), Class, Order, Family, Genus, Species.
- DNA (deoxyribonucleic acid): the molecule carrying genetic information; its double-helix structure was described by James Watson and Francis Crick (1953), building on Rosalind Franklin's X-ray work.
- Gene: a segment of DNA that codes for a particular character or protein.
- Chromosome: a thread-like structure of DNA and protein in the nucleus. Humans have 23 pairs (46 chromosomes); XX in females and XY in males, so the father's chromosome decides the child's sex.
- Genotype is the genetic make-up; phenotype is the visible expression.
- Gregor Mendel, the father of genetics, established the laws of inheritance (dominance, segregation, independent assortment) using garden pea plants. A dominant trait masks a recessive trait.
| Item |
Fact |
| Cell named by |
Robert Hooke (1665, in cork) |
| Living cells first seen by |
Anton van Leeuwenhoek |
| Nucleus discovered by |
Robert Brown (1831) |
| Cell theory |
Schleiden and Schwann (1838 to 1839); Virchow added new cells from old |
| Powerhouse of the cell |
mitochondrion (energy, ATP) |
| Site of protein synthesis |
ribosome |
| Suicide bag of the cell |
lysosome |
| Photosynthesis site |
chloroplast (plant cells only) |
| Control centre |
nucleus |
| Packaging and dispatch |
Golgi apparatus |
| Item |
Fact |
| Cell wall present in |
plant cells (not animal cells) |
| Five kingdoms proposed by |
R. H. Whittaker (1969) |
| Binomial nomenclature by |
Carolus Linnaeus (father of taxonomy) |
| Human binomial name |
Homo sapiens |
| DNA double helix described by |
Watson and Crick (1953) |
| Father of genetics |
Gregor Mendel (used pea plants) |
| Human chromosome number |
46 (23 pairs); XY male, XX female |
| Largest human cell |
ovum (egg) |
| Longest human cell |
nerve cell (neuron) |
| Smallest human cell |
sperm |
- Chloroplasts let green plants convert sunlight, water and carbon dioxide into food and oxygen by photosynthesis, the base of every food chain in environment and ecology.
- Understanding genes and chromosomes underlies the genetic-engineering and GM-crop work in biotechnology and genetics.
- Bacteria (kingdom Monera) include useful species (curd, antibiotics, nitrogen fixation) and harmful disease-causing ones, see nutrition diseases and health.
- DNA fingerprinting, which exploits the uniqueness of an individual's DNA, is a forensic mainstay for the CAPFs and police in criminal investigation, terror cases and victim identification.
- Microbial classification matters for biosecurity: distinguishing bacteria, viruses and protozoa guides outbreak response and CBRN defence.
Q1The "powerhouse of the cell" is the
- Aribosome
- Bnucleus
- Cmitochondrion
- Dlysosome. Answer:
- C. The mitochondrion releases energy as ATP through respiration.
Q2Which structure is present in a plant cell but absent in an animal cell?
- Anucleus
- Bribosome
- Ccell wall
- Dcell membrane. Answer:
- C. The cellulose cell wall (and chloroplast) is unique to plant cells.
Q3The five-kingdom classification was proposed by
- ALinnaeus
- BMendel
- CWhittaker
- DDarwin. Answer:
- C. R. H. Whittaker proposed it in 1969.
Q4The double-helix structure of DNA was described by
- AMendel
- BWatson and Crick
- CHooke
- DPasteur. Answer:
- B. Watson and Crick described it in 1953.
Q5A normal human body cell contains how many chromosomes?
- A23
- B44
- C46
- D48. Answer:
- C. Humans have 46 chromosomes in 23 pairs.
- Prokaryote versus eukaryote: prokaryotes (bacteria) have no true nucleus; eukaryotes (plants, animals, fungi, protists) do.
- Cell wall versus cell membrane: the cell membrane is in all cells; the rigid cell wall is only in plant, fungal and bacterial cells.
- Mitochondrion versus chloroplast: the mitochondrion releases energy (respiration, all cells); the chloroplast traps energy (photosynthesis, plant cells only).
- Gene versus chromosome: a chromosome is a long DNA thread carrying many genes; a gene is a short DNA segment coding for one trait.
- Genotype versus phenotype: genotype is the genetic make-up; phenotype is what is visible.
- Mendel versus Linnaeus: Mendel is the father of genetics; Linnaeus is the father of taxonomy.
- Organelle nicknames: mitochondrion is the powerhouse, ribosome is the protein factory, lysosome is the suicide bag, Golgi is the post office, nucleus is the brain of the cell.
- Plant-only trio to recall: cell Wall, Chloroplast, large Vacuole (W, C, V).
- Five kingdoms in order of complexity: Monera, Protista, Fungi, Plantae, Animalia.
- "XY makes a boY" to recall that the male is XY.
- Robert Hooke named the cell in 1665; the cell theory came from Schleiden and Schwann.
- Mitochondrion is the powerhouse, ribosome makes proteins, lysosome is the suicide bag, chloroplast does photosynthesis.
- Cell wall, chloroplast and a large central vacuole are unique to plant cells.
- Whittaker's five kingdoms (1969) are Monera, Protista, Fungi, Plantae, Animalia.
- Linnaeus gave binomial nomenclature (father of taxonomy); Mendel is the father of genetics.
- Watson and Crick described the DNA double helix in 1953; humans have 46 chromosomes (XY male, XX female).
- The cell is the basic unit of life; Robert Hooke named it in 1665 from cork.
- The cell theory says all life is cellular and new cells come from existing cells.
- Prokaryotes (bacteria) lack a true nucleus; eukaryotes have one.
- The mitochondrion is the powerhouse; the ribosome makes proteins; the lysosome is the suicide bag.
- Chloroplast, cell wall and a large central vacuole are unique to plant cells.
- The nucleus is the control centre and holds the chromosomes.
- Whittaker's five kingdoms are Monera, Protista, Fungi, Plantae and Animalia (1969).
- Linnaeus gave binomial nomenclature; the human binomial is Homo sapiens.
- The classification order is Kingdom, Phylum, Class, Order, Family, Genus, Species.
- Watson and Crick described the DNA double helix in 1953.
- A gene is a DNA segment coding for a trait; a chromosome carries many genes.
- Humans have 46 chromosomes (23 pairs); males are XY, females XX, and the father decides sex.
- Mendel, using pea plants, is the father of genetics; dominant traits mask recessive ones.
- The ovum is the largest human cell; the neuron is the longest; the sperm is the smallest.
- Cell: the basic structural and functional unit of all living things.
- Organelle: a specialised structure inside a cell with a specific function.
- Prokaryote: an organism whose cells lack a true membrane-bound nucleus (bacteria).
- Eukaryote: an organism whose cells have a true nucleus and membrane-bound organelles.
- Chlorophyll: the green pigment in chloroplasts that traps light for photosynthesis.
- Tissue: a group of similar cells performing a common function.
- Taxonomy: the science of classifying and naming living organisms.
- Binomial nomenclature: the two-part Latin naming system of genus and species.
- Gene: a segment of DNA coding for a particular character.
- Chromosome: a thread of DNA and protein carrying genes, found in the nucleus.
- Genotype: the genetic composition of an organism.
- Phenotype: the observable characteristics of an organism.
- Dominant trait: a trait that is expressed even when only one copy is present.
- Recessive trait: a trait expressed only when two copies are present.