Biology Notes

Living organisms share several key characteristics, including movement, respiration, sensitivity, growth, reproduction, excretion, and nutrition.
Movement: An action by an organism or part of an organism causing a change of position or place.
Respiration: Chemical reactions in cells that break down nutrient molecules and release energy for metabolism.
Sensitivity: The ability to detect or sense stimuli in the internal or external environment and to make appropriate responses.
Growth: A permanent increase in size and dry mass by an increase in cell number or cell size or both.
Excretion: Removal of the waste products of metabolism from organisms (chemical reactions in cells including respiration), toxic materials, and substances in excess of requirements.
Nutrition: Taking in of materials for energy, growth, and development; plants require light, carbon dioxide, water, and ions; animals need organic compounds and ions and usually need water.

Classification is the grouping of organisms according to their structural similarities. Organisms sharing similar features are placed in one group.
A classification system helps scientists sort organisms in order, identify new organisms by determining which group they fit into, and makes it easier to study organisms when they are sorted into groups.
Taxonomy, the technique of classifying organisms, is derived from the words 'Taxis' (arrangement) and 'Nomos' (method).
Carolus Linnaeus, a Swedish botanist, developed the modern taxonomic system.

Kingdom: Largest division of living things (e.g., Animal Kingdom or Plant Kingdom).
Phylum: Each kingdom is divided into smaller subdivisions called phyla (e.g., Chordates - individuals having the notochord).
Class: Phyla are separated into classes (e.g., Mammalia, Birds, Reptilia, and Amphibians).
Order: A group of related families (e.g., Carnivore).
Family: Classes are divided into families, which contain more than one genus.
Genus: Families are sub-partitioned into genera. Animals that have the same genus are fundamentally the same.
Species: Organisms of a particular kind whose members can interbreed among themselves to produce fertile offspring.
Mnemonic: Kinetic People Can Often Fetch Great Score

Plants can be divided based on whether they make seeds or not.
Plants that don't make seeds:
- Algae: Has no roots, stems or leaves structure
- Mosses: Has some roots, stems or leaves structure
- Ferns: Has roots, stems, and leaves
Plants that make seeds:
- Gymnosperms (no flowers) e.g., Conifers
- Angiosperms (flowers) e.g., Sunflower

Feature	Monocots	Dicots
Cotyledons	One	Two
Leaf Veins	Usually parallel	Usually netlike
Vascular Bundles	Usually complexly arranged	Usually arranged in a ring
Root System	Fibrous	Taproot
Floral Parts	Usually in multiples of three	Usually in multiples of four or five

Platyhelminthes (Flatworms):
- They have a flat, ribbon-like body.
- Body is bilaterally symmetrical.
- Body has a single opening.
- Most are parasites.
- Example: Tapeworms, Liverfluke.
Nematoda (Roundworms):
- They have a thread-like, rounded and unsegmented body.
- Body has two openings: mouth and anus.
- Most are parasites and reproduce sexually by laying eggs.
- Example: Pinworm, Ascaris.
Annelids (Segmented worms):
- They have a segmented bilaterally symmetrical body.
- They have a body cavity.
- They have special organs of excretion called Nephridia.
- Example: Earthworm, Leech.

Insects:
- Body is divided into head, thorax, and abdomen.
- Two pairs of wings attached to the thorax.
- Six jointed legs attached to the thorax.
- One pair of antennae on their head.
- Example: Cockroach
Arachnids:
- Have eight jointed legs.
- Do not have wings.
- Body divided into cephalothorax and abdomen.
- Examples: spiders, scorpions
Crustaceans:
- Tough exoskeleton.
- Have more than four pairs of jointed legs.
- Have two pairs of antennae.
- Examples: Lobsters, Crabs, woodlice.
Myriapods:
- Have one pair of antennae.
- Segmented bodies.
- Many legs.
- Eg. Centipede

Viruses are a connecting link between living and non-living.
They are non-cellular microbes composed of protein, nucleic acids, and lipids.
They are measured in nanometers with size ranging from $20$ nanometers to $250$ nanometers and could only be seen with an electron microscope.
They contain the core of nucleotides surrounded by a protein coat which could invade living cells.
They are active inside host cells and reproduce inside them by infecting living cells.

These can be unicellular or multicellular with the cell wall made of chitin.
These are heterotrophic and cannot synthesize their own food.
They comprise membrane-bound organelles.
Yeasts, molds, mushrooms are some of the important fungi.
They decompose dead plants and animals, extracting nutrients from them.
Few fungi are harmful and cause fungal infections like ringworm. The others are used in making antibiotics like penicillin.
Fungi such as yeast is also used in all baking industries and also in the beer and wine industries.

Bacteria are unicellular, microscopic, prokaryotic microbes that contain no true nucleus.
Their cell wall is made up of peptidoglycan. They have a flagellum that facilitates locomotion.
Bacteria are of different types depending on their shapes and sizes.
They reproduce through binary fission, transfer of genetic material through transformation, transduction and conjugation, and through sporulation.

It is the scientific method of writing the name of the organism using a two-part method.
The first part is the name of the genus to which the organism belongs, and the second part is the name of that particular species.
Such scientific names are underlined when handwritten and are in italics when typed.
This method was introduced by Carolus Linnaeus.
Binomial Nomenclature largely consists of two words – the first word beginning with a capital letter and known as genus (of the organism) and the second word begins with a lower case letter and defines the species of the organism.
Binomial Nomenclature must be written in italic and also known as scientific name.
For example, the binomial nomenclature of human is - Homo sapiens; tiger - Panthera tigris, etc.

Biologists previously relied on studying the morphology and anatomy of organisms to determine their relationships.
Now, DNA analysis is a powerful tool.
By comparing the sequences of bases (A, C, G, and T) in the DNA of different species, biologists can determine how closely related they are.
The more similar the base sequences, the more recently the species shared a common ancestor.
Similarities in amino acid sequences in proteins can also be used in the same way.