Biodiversity (Kingdom Animalia)

Phylum Porifera (Sponge)

– Water enters through porocytes & flow out through osculum.

 

Phylum Cnidaria (Obelia, jellyfish)

– Diploblastic

– Acoelomate

– No excretory cells (through mouth)

– Nerve nets

– Polymorphism –polyps reproduce medusa

Obelia: mesoglea layer, enteron

 

Phylum Platyhelminthes (Taenia, flatworms)

– Triploblastic

– Acoelomate

– Bilateral symmetry

– Unsegmented

– Has excretory & osmoregulatory system

– No circulatory system

– Hermaphrodite

Taenia: proglottid (repetitive units)

 

Phylum Nematoda (Ascaris, roundworms)

– Triploblastic

– Pseudocoelomate

– Bilateral symmetry

– Unsegmented

– Complete digestive system (mouth & anus)

– Longitudinal muscle

– Cuticle

– Separate sexes (unisexual)

 

Phylum Annelida (Class Oligochaeta(few setae per segment)—Pherethima, segmented worms)

– Triploblastic

– Coelomate

– Segmented

– Complete digestive system

– Closed circulatory system with haemoglobin

– Excretory system with nephridia

– Longitudinal & circular muscles

– Setae/chatae to aid movement

– Hermaphrodites

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Phylum Arthropoda

– Triploblastic

– Bilateral symmetry

– Chitinous exoskeleton

– Jointed appendages

– Open circulatory system (lymph)

 

Class Arachnida (Lycosa, spider)

– No antenna

– Protosoma & opisthosoma

– Lungs/trachae

– Simple eyes

 

Class Insecta (Periplaneta, cockroach)

-1 pair of antenna

– Head, thorax, abdomen

 

Class Crustacea (Penaeus, prawn)

– 2 pairs of antenna

– Cephalothorax, abdomen

– Gills

– 1 pair of stalked eyes

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Phylum Mollusca (Class Gastropoda–Helix, snail)

– Triploblastic

– Bilateral symmetry

– Ventral muscular foot

– Dorsal visceral mass

– Open circulatory system with haemolymph

– Excretion through nephridia

– Radula to scrape food

– Separate sexes

– Trochophore larva

 

Phylum Echinodermata (Holothuria, sea cucumber)

– Triploblastic

– Coelomate

– Bilateral symmetry (larva) ; Pentametric symmetry (adult)

– Water vascular system – tube feet

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Phylum Chordata

– Pharyngeal gill slits

– Post-anal tail

– Dorsal hollow nerve cord

– Notochord

 

Class Chondrichthyes (Carcharodon, shark)

– Cartilaginous skeleton

– Heterocercal fins

– Paired fleshy fins

– No operculum

– Lateral line system

– Placoid scales

– Internal fertilisation

 

Class Osteichthyes (Tilapia, fish)

– Bony skeleton

– Homocercal fins

– Paired bony/cartilagous fins

– Have operculum

– Have swim bladders

– Cycloid scales

– External fertilisation

– Oviparous

 

Class Reptilia (Naja, cobra)

– Amniotic & leathery egg

– No external ears

– Ectothermic

– Three chambered heart

– Internal fertilisation

– Dry scaly skin

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Biodiversity (Kingdom Prokaryotae, Protoctista, Fungi, Plantae)

Kingdom Prokaryotae (bacteria, cyanobacteria)

– Lack of nucleus & membrane-bounded organelles

– Some are photoautotrophs (cyanobacteria/blue-green algae)

– Circular DNA

– 70S ribosomes

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Kingdom Protoctista

 

Subkingdom Algae (Plant-like protists)

– Autotrophs (have chlorophyll)

– No true stem/leaves/root

 

Phylum Chlorophyta (Spirogyra, Chlamydomonas)

Phylum Zoomastigna (Euglena)

Phylum Phaeophyta (Fucus, brown algae)

 

Phylum Chlorophyta (Spirogyra, Chlamydomonas)

– Cell wall made of cellulose.

– Stores food as starch.

 

Phylum Zoomastigna (Euglena)

– Has pellicle to maintain its shape

– Stores carbohydrate as paramylum

– Has contractile vacuole

 

Phylum Phaeophyta (Fucus, brown algae)

– Stores laminarin

– Photosynthetic pigment is fucoxanthin

– Large thallus (holdfast, stipe, blade)

– Non-vascular

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Subkingdom Protozoa (Animal-like protists)

– Heterotroph

– Contractile vacuole

 

Phylum Rhizopoda (Amoeba)

Phylum Ciliophora (Paramecium)

 

Phylum Rhizopoda (Amoeba)

– Have contractile vacuole

– Pseudopodium

 

Phylum Ciliophora (Paramecium)

– Cilia

– Oral groove

– Macronucleus & micronucleus(reproduction)

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Kingdom Fungi

– Chitin cell wall

– Stores glycogen

– Heterotrophs (no chlorophyll)

– Non-motile

 

Phylum Zygomycota (Mucor)

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Kingdom Plantae

 

Phylum Bryophyta (Class Hepaticae—Marchantia)

– No true roots/stems/leaves

– Non-vascular

– Gametophyte generation is dominant (thallus) — attach to the substratum by rhizoid

– Antheridium & archegonium

– Water-dependent male gametes (antherozoids)

 

Phylum Filicinophyta (Ferns–Dryopteris)

– True stems & leaves

– Vascular (no xylem vessel, only tracheids)

– Sporophyte generation is dominant

– Sorus contains sporangium

– Water-dependent male gametes (antherozoids)

– Independent/free-living gametophyte generation (photosynthetic prothallus)

 

Phylum Coniferophyta (Pinus)

– Cones

– Ovules not protected by ovary

– Seed not protected by pericarp (naked seeds)

– Spores disperse by wind

– Vascular (no xylem vessels, no companion cell)

– Heterosporous

 

Phylum Angiospermophyta

– Flower: Male — Androecium (Stamen–anther, filament) ; Female — Gynaecium (Carpels–ovule, stigma, style)

– Heterosporous

– Protected seeds

– Double fertilisation

 

Class Dicotyledonae

– Vascular bundle in ring form

– Distinct cortex & pith

– Reticulate venation in leaves

– Show secondary growth

– Tap roots

– Floral divisible by 4 or 5

 

Class Monocotyledonae (Zea mays, corn/maize)

– Vascular bundles scattered

– No distinct pith/cortex

– No vascular cambium

– Parallel venation

– No secondary growth

– Fibrous roots

– Floral parts divisible by 3

– Petals & sepals not distinct

Natural Selection

What is natural selection?

A process whereby an organism which have well adapted characteristics to a particular environment will survive to a reproductive age to produce offspring.

Types of Natural Selection:-

1) Stabilising selection

The mean is selected for; the extreme phenotypes are selected against.

  • No change in average
  • Reduce genetic variation

Example: babies’ birth weights

2) Directional Selection

The selection of phenotype occurs at one end of the range of variation. The phenotype shifts either to the right or to the left.

  • A change in average
  • Reduce genetic variation

Example: beak shape

3) Disruptive Selection

Extreme phenotypes have selective advantage (be selected for; therefore not eliminated).

  • Genetic variation remains.

Example: beak length

4) Sexual Selection

  • Selection of specific phenotypes or mating behaviour occurs.
  • Usually female animal choose for certain appearance or behaviour.
  • To compete for healthy mate thus produce healthy offspring.

Example: only peacock with dazzling plumage and attractive mating behaviour is allowed to mate.

5) Polymorphism

A condition when a specific trait of a species exists in two or more different forms. (a result of multiple alleles)

Example: ABO blood system, patterns of snail shells, light/dark peppered moth

Ploidy

Ploidy refers the number of sets of chromosomes in a cell, e.g. haploid(n) & diploid(2n).
Euploidy refers to complete set(s) of chromosome, e.g. 23 or 46 or 69 chromosomes in human.
Aneuploidy is non-euploidy, i.e. one extra (Down’s syndrome) or one missing chromosome (Turner’s syndrome).Polyploidy is the state of having multiple sets of chromosomes (i.e. tetraploid, hexaploid); there are two types:-

Allopolyploidy/alloploidy is the doubling of chromosome sets in a hybrid species.

Autopolyploidy is the doubling of chromosome sets within the same species.

AIDS (Acquired Immunodeficiency Syndrome)


note: numbers are not in accordance to the diagram above.

1) Binding
Glycoprotein of HIV (gp120) binds to the coreceptor CD4 of helper-T cell.
2) Insertion
The phospholipid bilayer of HIV fuses with the plasma membrane of helper-T cell, to insert capsid into the helper-T cell.
3) Uncoating
Capsid is broken down by hydrolysis (require enzyme from virus), releasing viral RNA and reverse transcriptase into the cytoplasm of helper-T.
4) Synthesis of DNA from RNA
Reverse transcriptase transcribes the single-stranded RNA codon by codon (A-T, G-C, etc.) to form a single-stranded DNA. The single-stranded DNA is then copied by reverse transcriptase to form a double-stranded DNA.
5) Integration
The double-stranded DNA moves into the nucleus to be integrated into the host genome/chromosome. The viral genome will replicate along when the cell replicate.
6) Transcription
The viral DNA is transcribed inside the nucleus of helper-T cell to form mRNA.
7) Translation
Viral mRNA diffuse out of nucleus. The viral components are synthesised actively using raw materials from the host (helper-T).
8) Assembly
The viral components that are newly synthesised are being assembled into a complete cell.
9) Extrusion
The daughter virus buds off from the helper-T cell.
10) Maturation
This new virus released will later mature and infect other cells in the body.

HIV can destroy helper-T, B-cells and macrophage (because they have CD4 coreceptor). As a result, various pathogen enters and infect body cells. The immune system of the patient is weakened.

Symptoms of HIV Infection:-
Frequent fever & diarrhea
Prolonged headache
Muscle & joint aches
Mouth thrush (fungal infection)
Pneumonia (bacterial infection on lungs)

Immune Responses

Cell-mediated Immune Response
1) Presentation of viral antigen on macrophage
Virus enters the body. Macrophage engulfs the virus. The virus is partly digested. A fragment of it is brought to the cell surface to be placed at the MHC-II protein. The complex formed is called antigen-MHC-II complex.
2a) Recognisation of antigen on macrophage by helper-T cell
Helper-T recognises the antigen on the MHC-II protein and binds with the macrophage by CD4 coreceptor. Then this binding stimulates macrophage to release interleukin-1. Then interleukin-1 stimulates helper-T to produce interleukin-2.
2b) Recognisation of antigen on infected cell by cytotoxic-T cell
Meanwhile cytotoxic-T cell recognises viral antigen on the MHC-I protein of the infected cell by CD8 coreceptor.
3) Proliferation & action of cytotoxic-T cell
Interleukin-2 (from step 2a) stimulates the proliferation of cytotoxic-T cell. Some of the cytotoxic-T cells become memory-T cells while some become effector-T cells. Cytotoxic-T cells secrete perforin to create pores on the infected cell. The infected cell is then destroyed by the pores that cause the cell content to leak out, shrinks, or burst.

Humoral Immune Response
Step 1 & 2a are identical.
2b) Presentation of viral antigen on B-cell
Meanwhile the free-floating viral antigens bind to the antibody on the surface of B-cell. B-cell takes in this antigen, digested it, and a fragment of this antigen is placed on MHC-II.
3) Recognisation of antigen on B-cell by helper-T cell
Helper-T recognises the antigen on MHC-II protein on B-cell. The binding stimulates helper-T to produce interleukin-2.
4) Proliferation of B-cells
Interleukin-2 released from helper-T then stimulates B-cells to proliferate. Some of the B-cells become plasma cells while some becomes memory-B. Memory-B will proliferate faster when encountering the same pathogen for the second time.
5) Production & action of antibodies
Plasma cells will produce antibodies. The antibodies are released into the bloodstream, and is brought to the site of infection. They can agglutinate the bacteria, thus many bacteria can be engulfed at the same time.

Theories of Evolution

What is evolution?

– Evolution is the change of alleles/genes in a gene pool of a population.

– As such a new species arose from a pre-existing species.

– All species have evolved from one common ancestral type.

– Natural selection provides the mechanism for one species to change into another.

– The gradual change of living things from one form into another over the course of time, the origin of species and lineages by descent of living forms from ancestral forms, and the generation of diversity.

Lamarck’s Theory (earlier theory, proven wrong later by scientists)

– Evolution occurred through the inheritance of acquired traits.

– Environmental pressure on an organism produces the specific needs in the organism to develop certain structures, characteristics or adaptations.

– The organism will act to fulfill its specific need.

– As a response to its actions, adaptations occur to the organism according to its specific need.

– The adaptations are transmitted from generation to generation.

Example:

– Giraffes with long necks resulted when the ancestors of the present giraffes ate leaves of trees instead of grass.

– To reach the leaves high up the trees, they have to stretch their necks.

– Continuous stretching of the giraffe’s neck produces giraffe with long necks.

– The longer necks that developed were then inherited by the giraffes’ descendants.

Lamarck’s theory is not accepted because the acquired characteristics cannot be inherited.

The acquired traits only involve changes in the phenotype, while the genootype of an organism is not affected.

Darwin-Wallace’s Theory

– Evolution occurs through natural selection.

– Natural forces select for the survival of organisms that are best fit in an environment.

– A population has high biotic potential produces more progeny than can be accommodated by the environment.

– An environment has a specific carrying capacity and can only support a specific number of organisms.

– Members of the population compete for survival.

– The members in a species show variations.

– Progeny that have the phenotype that is best adapted to the environment have more chance to survive, reproduce and to pass genes to offspring.

– Progeny with phenotypes that are not suited to the environment will die before reaching the reproductive age.

– Over time, the frequency of phenotype that gives the best adaptations to survive in an environment increases.

– Survival of the fittest occurs.

Example:

– In a population of giraffes, there is variation for the length of giraffe’s neck.

– Giraffes with longer neck are selected by the environment as the giraffes are able to reach leaves on taller trees.

– Longer neck giraffes obtain higher food supply compared to giraffes with shorter neck.

– Giraffes with long necks survive and have higher chance to reproduce, passing gene for long neck to offspring.

– Giraffes with shorter neck die at a younger age as it obtains less food supply, and lower chance to reproduce to pass genes to the next generation.

– The process is repeated over many generations to produce modern giraffes with long necks.