GCSE Science/Genetics

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Biodiversity

Biodiversity is a measure of the variety of living organisms within a particular habitat, ecosystem, biome, or all over Earth.

The Binomial System:

The Binomial System of scientifically naming organisms was developed by Carl Linnaeus of Sweden. It consists of the organism’s Genus and Species name, and thus it is called as Binomial. It consists of 7 levels:

• Kingdom
• Phylum
• Class
• Order
• Family
• Genus
• Species

Eukaryotes

As seen in the diagram above, Eukaryotes consist of Protoctists, Fungi, Plant, and Animal kingdoms.

Protoctists

are organisms with a nucleus, and many flexible organelles amongst their species (for example, some have chloroplasts and cell walls like plants and some like animal cells without these distinguishing characteristics). Their main characteristics include:

• Unicellular or multi-cellular bodies
• Cells with or without cell wall and chloroplasts
• Some species are autotrophic, rest are heterotrophic
• All species have cells with nucleus

Examples of Protoctists:

• Paramecium
• Chlamydomonas
• Seaweeds

Fungi

Fungi are organisms which do not have chlorophyll, thus are heterotrophic and feed on dead organic matter parasitically. The most common known is the edible mushroom; others include fungi  causing diseases like athlete’s foot, ringworm, panama disease etc.Their characteristics include:

• Multicellular bodies (very few are unicellular)
• Have nuclei
• Reproduce by spore production
• Are heterotrophic
• Don’t have chloroplasts
• Feed by parasitic or saprophytic means on organic dead matter

Examples include:

• Saccharomyces cerevisiae
• Penicillium
• Mushroom

Animals

Within the Animal Kingdom, there are several phylums such as Arthropods,

Phylum Arthropoda

• Hard exoskeleton
• Segmented bodies
• jointed appendages
• exoskeleton composed of protein and chitin
• Open circulatory systems in which heart pumps hemolymph through short arteries into open spaces (sinuses)
• Aquatic members have gills for gas exchange
• terrestrial members have tracheal system of branched tubes leading from their surface throughout body

Class Crustaceans

• More than 4 pairs of jointed legs
• Breathe through gills
• Antennae present
• Mostly marine

Examples of crustaceans: Crabs, lobsters etc.

Class Arachnids

• With 4 pairs of jointed legs
• Breathe through gills and book lungs
• Mostly terrestrial

Examples of arachnids: Scorpion, spider etc.

Class Insects

• Have 3 pairs of jointed legs
• Have 2 pairs of wings
• Breathe through trachea
• Antennae present
• Mostly terrestrial

Examples of insects: Locust, Moth, House Fly, Grasshopper etc.

Class Myriapods

• Their nervous system has encephalon (brain) and a spinal cord.
• The encephalon is placed inside the skull and spinal cord is placed inside the spine.

Class Fish

• Are cold blooded
• Have streamlined bodies
• Aquatic
• Have scales on their bodies
• May be Herbivores or Carnivores
• Lay eggs in water
• Have fins
• Breathe through gills

Example of Fish: Mackerel, Pomfret, Tuna, Salmon etc.

Class Amphibians

• Give birth to offspring by laying eggs
• Have 4 limbs
• Their habitat is both terrestrial and aquatic
• Have moist skin
• Breathe through gills when young; when mature, breathe through lungs
• Adult often lives on land

Example of Amphibian: Frog, Salamander etc.

Class Reptiles

• Have scales on body
• Are cold blooded
• Terrestrial
• Lay eggs to give birth to offsprings
• Egg shells are rubbery

Examples of Reptiles: Lizard, Snake etc.

Class Birds

• Don’t have teeth, instead have a beak
• Have hollow bones
• Are warm blooded
• Lay hard shelled eggs
• Forelimbs replaced by wings
• Breathe through lungs

Examples of Birds: Flamingo, Eagle, Hawk, Sparrow etc.

Class Mammals

• Warm blooded
• Can maintain a constant body temperature
• Have different types of teeth
• Have skin covered by Hair
• Give birth to live young offsprings
• Have sudoriferous (sweat) glands
• Females have mammary (milk secreting) glands that produce milk to feed young ones.

Example: Human being

The Plant Kingdom

Phylum Angiosperm:

• Have root, stem and leaves
• Have xylem and phloem
• Reproduce by seed production
• Seeds are produced inside the ovary of the flower
• Phloem: Transports sugar
• Xylem: Transports water and minerals

Plant Part	Monocot	Dicot
Root System	Adventitious root only	Adventitious root, Taproot or both
Cotyledons	One	Two
Stem	Vascular bundles scattered	Vascular bundles arranged in a ring
Leaves	Exhibit parallel venation	Exhibit reticulate venation
Flower	Either trimerous, tetramerous, seldom pentamerous	Either pentamerous, tetramerous, seldom trimerous

Viruses

• Entirely microscopic
• Consisting of a single nucleic acid surrounded by a protein coat
• Capable of replication only within living cells of bacteria, animals or plants.

Example of Viruses: Coronavirus, Human Immunodeficiency Virus, Tuberculosis, etc.

Prokaryotes

Bacteria are prokaryotic and unicellular. they have cell walls and circular DNA called plasmids. They are Heterotrophs or Autotrophs.

Example: L.bulgaricus