Question

What is a plant? Provide a thorough answer that clearly defines plants and highlights their synapomorphies. Define key terms in your own words. In your answer, also distinguish plants from their closest living relatives.

Answer 1

Ans. A Plant is mainly a multicellular eukaryotic organism and most plants perform photosynthesis to produce their own food.

Characteristics of plant cell which differentiates it from animal cells are follows:-

1. Plant cells have cell wall while it is absent in animal cells.

2. Generally plant cells have plastids which contain chloroplast/chlorophyll to perform photosynthesis,while they are absent in animals.

3. Plant cells have large central vacuole which is absent in animals.

All organisms which belong to kingdom plantae are plants and they are divided into five groups/divisions which are follows:-

1. Algae

2.Bryophytes

3.Pteridophytes

4.Gymnosperms

5.Angiosperms

Although mainly plants are multicellular,but some unicellular plants are also present.

e.g. Volvox is a algae and have some unicellular species which may live by forming colony of hundreds/thousands or may live separately.

Plants are predominantly photosynthetic,but there are some parasitic and saprophytic plants which do not make their own food and depend on other plants/saprotrophs.

e.g. Cuscuta is a parasitic plant which do not perform photosynthesis.

Synamorphies: They are unique evolutionary characteristics of plants which are also shared by their ancestors/evolutionary descendants.

Some examples are follows:-

1. Presence of chloroplast in plant cell is best example of synamorphy,as it comes from cyanobacterium when a eukaryote engulf cyanobacterium and managed to escape phagocytic vacuole of host cell by endosymbiotic event/endosymbiosis. Later these cells develop to plants.

2. Green algae are considered as sister taxa to all land plants,thus an example of synamorphies.

3.In land plants multicellular sporophyte,protected embryo,etc are examples of synamorphies.

4. Presence of seed habit in pteridophytes is an example of synamorphy.

5. Presence of stomata for gaseous exchange is also an example of synamorphy in all land plants except liverworts.

6.Presence of chlorophyll b and storage of starch is example of synamorphy in all green plants.

Green algae are considered as closest living relatives of plants,but due to absence of true root,stem and leaves they are not true plants.

Kingdom protista do not have discrete boundaries and what may be a photosynthetic protistan to one biologist may be a plant to another.In this kingdom Euglenoids are much similar to plants and are photosynthetic in presence of sunlight and becomes heterotrophs in absence of sunlight,but as they don't have cell wall,thus classified under protista.

Further true root, stem and leaves are characteristic features of true plants.

Root: Generally they are below the surface of soil and provide adherence,minerals and water to plants.

Stem:It is structural axes of a vascular plants as the root.It supports leaves,flowers and fruits.

Leaves: They are green lateral appendage of stem,have stomata and  mainly involves in photosynthesis .

Flower: It is reproductive structure of flowering plants and after fertilization of male and female gametes ovary of plant develops to fruits.