Classification

Question 1

There are three domains. They are;

Answer 1

a) Domain – Bacteria- consists of one kingdom. Kingdom - Bacteria
b) Domain –Archaea-consists of one kingdom. Kingdom - Archaebacteria c) Domain –Eukarya-consists of four kingdoms.
Kingdom - Protista Kingdom - Fungi Kingdom - Plantae Kingdom -Animalia

Question 2

Key characteristics of Domain Bacteria

Answer 2

• They are prokaryotic
• They are unicellular, colonial, filamentous
• Most of them are found in size between 0.5 to 5μm
• Well adapted to most of the ‘normal’ habitats (both land and water)
• Most of them contain peptidoglycan in their cell walls
• According to the amount of peptidoglycan present in the cell wall they are classified as Gram positive and Gram negative bacteria
• Most of their cell walls are surrounded by a sticky layer of polysaccharides or proteins called capsule
• Most of them have flagella for motility. Bacterial flagellum differs from eukaryotic flagellum as they are not covered by a plasma membrane and absence of 9+2 structure of microtubules.
• Possess diverse nutritional modes-Autotrophs, heterotrophs
• Posses diverse metabolic modes- obligate aerobes, obligate anaerobes, facultative anaerobes, etc.
• Some are capable of performing nitrogen fixation- e.g. Rhizobium sp., some cyanobacteria
• Rapid reproduction by binary fission. Some perform conjugation as a sexual method.
• Certain bacteria use bacterial chlorophyll as a photosynthetic pigment.

Question 3

Key Characteristics of Cyanobacteria

Answer 3

• Prokaryotic organisms
• Photosynthetic
• Most are unicellular and oxygen generating and solitary. But some are linked to form filaments or colonies sheathed in mucous
• Some have the ability of fixing atmospheric nitrogen

Question 4

Key characteristics of Domain Archaea

Answer 4

• They are prokaryotic and unicellular.
• They lack peptidoglycan in their cell walls which are made up of proteins and polysaccharides
• The size of most of them is between 0.5-5 m
• They include extreme halophiles and extreme thermophiles
• Some Archaeabacteria live in more moderate environments-Methanogens
• Other species inhabits the anaerobic guts of cattle, termites and other herbivores

Question 5

Key characteristics of Domain Eukarya

Answer 5

• They are Eukaryotic
• Vary in size
• Most of them are multicellular
• Habitats are diverse
• Diverse in nutrition
• Mostly aerobes
• Most of them exhibit sexual reproduction (some protists are only known to reproduce asexually)

Question 6

Table 3.1: A comparison of the three domains of life

Characteristic
Bacteria
Archea
Eukarya

Answer 6

1
Cellular organization
Prokaryotic
Prokaryotic
Eukaryotic

2
Cell wall composition
Peptidoglycan
Proteins and polysaccharides (lack peptidoglycan)
Cellulose, Hemicellulose, Pectin and Chitin

3
Membrane lipids
Unbranched hydrocarbons
Some branched hydrocarbons
Unbranched hydrocarbons

4
Genetic Composition
Histones associated with DNA
Absent
Present in some species
Present

Circular chromosomes
Present
Present
Absent

Introns in genes
Very rare
Present in some genes
Present in many genes

5
Protein synthesis

RNA polymerase
One kind
Several kinds
Several kinds

Initiator amino acids for protein synthesis
Formyl- methionine
Methionine
Methionine

6
Response to antibiotics  -Streptomycin
and Chloramphenicol
Growth inhibited
Growth not inhibited
Growth not inhibited

7
Growth at temperatures > 100 ̊C
No
Some species
No

8
Habitats
Diverse habitats
extreme environmental conditions-volcanic pits/ hot springs/ salt marshes etc.
Diverse habitats

9
Examples
Bacteria, Escherichia coli, Salmonella typhi
cyanobacteria; Nostoc, Anabaena ,,

Archaebacteria;
Methanococcus Thermococcus.,
Halobacteria .

Protists fungis
plants and animals

Question 7

Key characteristics of Kingdom Protista

Answer 7

• Most of them are unicellular, although there are some colonial and multi cellular species
• It is a polyphyletic group (originated from more than one ancestor) and an artificial group in classification.
• Found in freshwater, marine and damp soil, some are symbionts.
• Unicellular, colonial or multicellular.
• Some are photoautotrophs, some are heterotrophs and some are mixotrophs (combination of photoautotrophic and heterotrophic nutrition).

Question 8

Euglena

Answer 8

• Unicellular, lack cell wall and pellicle present.
• Chloroplasts are present.
• They have one or two flagella
• They have eye spot
• Contractile vacuole is present
• They have a pocket at one end of the cell from which one or two flagella emerged.

Question 9

Paramecium

Answer 9

• Habitat is freshwater
• Lack cell wall but pellicle is present, unicellular
• Cilia may completely cover the cell surface
• They have two types of nuclei- mega nucleus and micronucleus
• Contractile and food vacuoles are present
• Oral groove is present

Question 10

Amoeba

Answer 10

• Aquatic (marine and freshwater) forms are free living, others are parasitic.
• Lack cell walls, unicellular organisms
• They form pseudopodia which are used to locomote and feed
• They do not have definite shape.
• Food vacuoles are present

Question 11

Ulva

Answer 11

• Macroscopic marine forms.
• Cell wall present
• Multicellular thallus differentiated into leaf like blades and root like holdfast.
• Green in colour (green algae)

Question 12

Gelidium

Answer 12

• Marine.
• Cell walls present
• Multicellular thallus with hold fast.
• It is greenish red in colour (red algae)

Question 13

Sargassum

Answer 13

• Marine
• Comparatively larger and complex
• Thallus is plant- like; it consists of a root like holdfast ,stem like stipe and leaf like blade.
• Multi cellular, thallus is supported by gas filled bulb shape floats.
• Appear in olive green or brown colour (brown algae)

Question 14

Diatoms

Answer 14

• It is aquatic (fresh water and marine)
• Unicellular, having glass like, wall consists of two parts that overlap (presence of silica)
• Highly diverse group regarding the shape and markings in the surface
• Golden brown in colour (golden brown algae)

Question 15

Kingdom Plantae

Evolutionary relationships among major groups of plants

Answer 15

It is believed that members of the kingdom Plantae were evolved from a group of chlorophytes/ green algae. Most of them are terrestrial organisms.

Chlorophyte algae lack key traits of land plants,
1.walled spores produced in sporangia,
2.multicellular gametangia,
3.dependent embryo and
4.apical meristem. They evolved in the terrestrial environment.
Plant groups can be distinguished based on the presence or absence of an extensive system of vascular tissue. Based on that there are two major groups of plants the can be seen; they are Vascular plants and Non-vascular plants.

Question 16

Diversification of Kingdom Plantae

Answer 16

Non-vascular plants
• Phylum Hepatophyta- Marchantia
• Phylum Bryophyta - Mosses- Pogonatum
• Phylum- Anthocerophyta- Anthoceros
Vascular seedless plants
Phylum – Lycophyta- Selaginella 
Phylum – Pterophyta- Nephrolepis

Vascular seed plants

• Gymnosperms- Phylum – Cycadophyta (Cycas sp.), - AUS
Phylum- Coniferophyta (Pinus ), NA
Phylum – Gnetophyta (Gnetum ) SA
• Angiosperms- Phylum – Anthophyta (all flowering plants)

Question 17

Non-vascular plants

Answer 17

One way to distinguish a group of plants is to see whether or not they have an extensive system of vascular tissue that transport water and nutrients throughout the plant body.
Most present day plants do have a complex vascular tissue system and therefore, are called vascular plants.
do not have an extensive transport system are described as non vascular plants.
Non vascular plants are informally named as Bryophytes.
e.g. Marchantia, Pogonatum, Antheroceros

Bryophytes share some derived traits with vascular plants, but lackin many innovations
of vascular plants such as
presence of true stems (not in seedless vascular ones),
roots and
leaves.

Question 18

Diversity of Bryophytes

Answer 18

Phylum- Hepatophyta e.g. Marchantia (liverworts).
Phylum Bryophyta e.g. Pogonatum (mosses)
Phylum Anthocerophyta e.g. Anthoceros (hornworts)

Characteristic features of phylum Bryophyta

e.g. Pogonatum
• Especially common in moist terrestrial places.
• Haploid gametophyte is dominant stage of the life cycle, photosynthetic and independent.
• Gametophytes are differentiated into ‘leaves’, ‘stems’ and rhizoids. They have no vascular tissues. Archegonia and antheridia are typically carries on separate female and male gametophyte. Therefore gametophyte is dioecious.
• Male plant produces flagellated sperm which can swim through a film of water for fertilization.
• Sporophytes are usually green and photosynthetic when young. However, they are not independent. They attach to their parental gametophytes and absorb nutrients and water from the female gametophyte.
• Sporophytes have specialized pores called stomata which are also found in all vascular plants.
• They are homosporous.

Question 19

Vascular plants cover about 93% of the existing plant species.
They can be further divided into two groups.

Answer 19

1. Seedless vascular plants
2. Seed plants

Seedless vascular plants
Seedless vascular plants lack seeds and disperse by means of spores. They are categorized into two groups.
1. Lycophytes 2. Pterophytes
Even though, both pterophytes and lycophytes are seedless plants, pterophytes share a more recent common ancestor with seed plants.
Fossils and living seedless vascular plants provide evidence for plant evolution during
Devonian and Carboniferous periods. The ancestors of vascular plants already have had some derived traits of modern vascular plants; however, they lack roots and some other adaptations.
Fossils suggest that, the ancestors of vascular plants had gametophyte and sporophytes that were about equal in size. However among the living vascular plants sporophyte generation is large and more complex. For example in ferns, leafy plants are the sporophytes

Question 20

Significant features of seedless vascular plants;

Answer 20

1. Transportation through Xylem and Phloem
   Vascular plants have two types of vascular tissues; Xylem and Phloem
   Xylem consists of tracheids, fibers and parenchyma cells- conducts water and minerals.
   Cell walls of tracheids and fibers are strengthened by the polymer lignin. These tissues permit plants to grow tall. This may facilitate them to obtain a high amount of light for photosynthesis and ease the spore dispersal.
   Phloem- this tissue has cells arranged in tubes. They distribute sugars, amino acids and other organic products among different parts of the plant.
2. Evolution of roots
   Roots are organs that absorb water and nutrients from the soil. They anchor the plants and allow the shoot system to grow taller. They are to replace the rhizoids seen in bryophytes. Root tissues of living plants resemble stem tissues of the early vascular plants preserved in fossils.
3. Evolution of leaves- There are two types of leaves. They are microphylls and megaphylls. Microphylls are single veined and smaller in size while megaphylls are large, flattened with branched veins.
   Leaves with branched vascular tissues increase the surface area for efficient photosynthesis (megaphylls).

Sporophylls and spore variations
Modified leaves that bear sporangia are known as sporophylls. Most seedless vascular plant species produce one type of sporangium and one type of spores. Therefore, they are known as homosporous.
Some plant species produce two types of sporangia and produce two kinds of spores called mega spores and microspores. This condition is known as heterosporous. Mega spores develop into female gametophyte while microspores develop into male gametophyte.