Classification- Plant Kingdom
In the previous chapter, we discussed Whittaker's Five Kingdom classification which includes Monera, Protista, Fungi, Animalia, and Plantae. In this chapter, we will focus on the plant kingdom, also known as Kingdom Plantae.
It is important to note that our understanding of the plant kingdom has evolved over time. Fungi, Monera, and Protista with cell walls are no longer considered part of Plantae. As a result, cyanobacteria, also known as blue-green algae, are not classified as algae anymore. In this chapter, we will discuss the following groups within Plantae:
Algae
- A diverse group of aquatic organisms capable of photosynthesis
Bryophytes
- Non-vascular plants that include mosses, liverworts, and hornworts
Pteridophytes
- Vascular plants without seeds, such as ferns and horsetails
Gymnosperms
- Seed-producing vascular plants with naked seeds, like conifers and cycads
Angiosperms
- Flowering plants that produce seeds enclosed within a fruit
Early Classification Systems in Angiosperms:
- Used superficial morphological characters like habit, colour, shape of leaves, etc.
- Based on vegetative characters or androecium structure (Linnaeus system).
- Artificial systems separated closely related species due to limited characteristics.
- Equal weightage given to vegetative and sexual characteristics, not ideal as vegetative characters are more affected by the environment.
Natural Classification Systems:
- Developed based on natural affinities among organisms.
- External and internal features considered, such as ultrastructure, anatomy, embryology, and phytochemistry.
- George Bentham and Joseph Dalton Hooker proposed a natural classification for flowering plants.
Chlorophyceae: Green Algae
- Commonly known as green algae
- Plant body can be unicellular, colonial, or filamentous
Colour and Pigments
- Usually grass green due to dominance of chlorophyll a and b
- Pigments localised in definite chloroplasts
Chloroplast Shapes
- Discoid, plate-like, reticulate, cup-shaped, spiral, ribbon-shaped
Storage Bodies: Pyrenoids
- One or more pyrenoids in chloroplasts
- Contain protein and starch
- Some algae store food as oil droplets
Cell Wall
- Rigid cell wall made of inner cellulose layer and outer pectose layer
Vegetative Reproduction
- By fragmentation or spore formation
Asexual Reproduction
- Flagellated zoospores produced in zoosporangia
Sexual Reproduction
- Isogamous, anisogamous, or oogamous
- Variation in type and formation of sex cells
Common Green Algae Examples
- Chlamydomonas, Volvox, Ulothrix, Spirogyra, Chara
MCQs with Solutions:
1. What is the common name for members of Chlorophyceae?
a. Red algae
b. Green algae
c. Blue algae
d. Brown algae
Answer: b. Green algae
2. Which pigments are dominant in green algae?
a. Chlorophyll a and b
b. Carotene and xanthophyll
c. Phycobilin and phycoerythrin
d. Fucoxanthin and chlorophyll c
Answer: a. Chlorophyll a and b
3. What are the storage bodies in chloroplasts called?
a. Chlorophyll
b. Pyrenoids
c. Granules
d. Vacuoles
Answer: b. Pyrenoids
4. What type of cell wall do green algae have?
a. Cellulose and pectin
b. Chitin and cellulose
c. Cellulose and pectose
d. Pectin and chitin
Answer: c. Cellulose and pectose
5. Which of the following is NOT a type of sexual reproduction in green algae?
a. Isogamous
b. Anisogamous
c. Oogamous
d. Autogamous
Answer: d. Autogamous
Location and Appearance
- Primarily found in marine habitats
- Vary in size and form, from simple branched to profusely branched
- Examples include Ectocarpus, Dictyota, Laminaria, Sargassum, and Fucus
Colour and Pigments
- Colour ranges from olive green to various shades of brown
- Depends on the amount of fucoxanthin, a xanthophyll pigment
- Contain chlorophyll a, c, carotenoids, and xanthophylls
Food Storage and Cell Structure
- Store food as complex carbohydrates, like laminarin or mannitol
- Vegetative cells have a cellulosic wall with gelatinous algin coating
- Protoplast contains plastids, a central vacuole, and nucleus
Plant Body Structure
- Attached to the substratum by a holdfast
- Has a stalk, called the stipe, and a leaf-like photosynthetic organ, called the frond
Reproduction Methods
- Vegetative reproduction occurs by fragmentation
- Asexual reproduction involves biflagellate, pear-shaped zoospores with two unequal flagella
- Sexual reproduction can be isogamous, anisogamous, or oogamous
- Union of gametes occurs in water or within the oogonium for oogamous species
- Sexual reproduction involves pyriform, pear-shaped gametes with two laterally attached flagella
What are Red Algae?
- Red algae, also known as Rhodophyceae, are named so due to the red pigment, r-phycoerythrin in their bodies.
- They are predominantly found in the marine environments, especially in warmer areas.
Where are they found?
- Red algae can be found in well-lit regions close to the water surface.
- They can also be found at great depths in oceans where little light penetrates.
Characteristics of Red Algae
- Most red algae have multicellular thalli.
- Some species have complex body organisations.
- They store food in the form of floridean starch, which is similar to amylopectin and glycogen in structure.
Reproduction in Red Algae
- Vegetative reproduction occurs through fragmentation.
- Asexual reproduction happens by non-motile spores.
- Sexual reproduction involves non-motile gametes and is oogamous, meaning it involves a large, immobile egg and small, mobile sperm.
- Post-fertilisation development is complex.
Common Members of Red Algae
- Polysiphonia
- Porphyra (Figure 3.1c)
- Gracilaria
- Gelidium
