BIOLOGY 2 Marks Questions

Isogamy: It is a type of sexual reproduction involving the fusion of morphologically-similar gametes. This means that the gametes are of the same size, but perform different functions. This type of reproduction is commonly observed in Spirogyra.

Archegonium: It is the female sex organ present in bryophytes, pteridophytes, and gymnosperms. In bryophytes and pteridophytes, it generally has a swollen venter and a tubular neck, and contains the female gamete called the egg.

	Homosporous pteridophytes	Heterosporous pteridophytes
1.	They bear spores that are of the same type.	They bear two kinds of spores – microspores and megaspores.
2.	They produce bisexual gametophytes.	They produce unisexual gametophytes.

Reduction divisions in the life cycle of a liverwort, a moss, a fern and a gymnosperm take place during the production of spores from spore mother cells. In case of an angiosperm, the reduction division occurs during pollen grain formation from anthers and during production of embryo sac from ovule.

Antheridium: It is the male sex organ present in bryophytes and pteridophytes and is surrounded by a jacket of sterile cells. It encloses the sperm mother cells, which give rise to the male gametes.

Sporophyll: In pteridophytes, the sporophytic plant body bears sporangia. These sporangia are subtended by leaf-like appendages known as sporophylls. In gymnosperms, microsporophylls and megasporophylls are found. These bear microspores and megaspores respectively.

Protonema: It is the first stage in the life cycle of a moss, developing directly from the spore. It consists of creeping, green, branched, and often filamentous structures.

	Syngamy	Triple fusion
1.	It is the process of fusion of the male gamete with the egg in an angiosperm.	It is the process of fusion of the male gamete with the diploid secondary nucleus in an angiosperm.
2.	A diploid zygote is formed as a result of syngamy.	A triploid primary endosperm is formed as a result of triple fusion.

Diplontic: It is the term used for the life cycles of seed-bearing plants (gymnosperms and angiosperms). In these plants, the diploid sporophyte is dominant, photosynthetic, and independent. The gametophyte is represented by a single-celled (or a few-celled) structure.

External features of dicotyledons:

1. Tap root system.
2. Two cotyledons in seeds.
3. Reticulate venation in leaves.
4. Tetramerous or pentamerous flowers.

1. Lycopodium/ Selaginella.
2. Dryopteris/ Pteris.

1. The plant body or the dominant phase in the life cycle is a sporophyte, which is differentiated into true roots, stem and leaves.
2. All these organs possess well-differentiated vascular tissues.
3. Sporophylls bear sporangia, in which spores are produced by meiosis in spore mother cells; sporophylls may be arranged into compact structures, called strobili or cones.
4. Each spore germinates (by mitosis) into a multicellular, inconspicuous, autotrophic structure, called prothallus, the gametophytic phase.
5. The prothallus bears antheridia and archegonia, where the male and female gametes are produced.
6. Water is essential for fertilisation and the zygote develops into the sporophyte.

Salient features of artificial classification system are:

1. They uses only gross superficial morphological characters such as habits, colours, numbers and shapes of leaves, etc.
2. These consider mainly the vegetative characters or the androecium characters as given by Linnaeus.
3. They separated closely related species.

1. Haploid phase.
2. Meiosis occurs during the germination of zygote.

The zygote is produced by the process of syngamy and the other male gamete fuses with the secondary nucleus to form the triploid Primary Endosperm Nucleus (PEN). In angiosperms, the astrological nature of the endosperm is triploid (3n). In the triploid condition, each nucleus has three sets of chromosomes.

1. Numerical taxonomy considers all the hundreds of observable characters and all characters are given equal weightage.
2. Number and codes are assigned to all the characters and the data are then processed using computers.

Two advantages of artificial system of classification are:

1. Artificial system is very easy to remember as it uses only one or a few characters for comparison.
2. It is practical and is akin to use of keys for identification of various taxa.

Habit and Habitat of Algae: Algae are chlorophyll-bearing, simple, thalloid, autotrophic and largely aquatic (both fresh water and marine) organisms. They occur in a variety of other habitats: moist stones, soils and wood. Some of them also occur in association with fungi (lichen) and animals (e.g., on sloth bear).

Flowers are of ornamental value for humans and they serve a larger purpose for plants as well as for humans. Colours in flowers are meant to attract agents of pollination from the animal world. As this facilitates cross pollination so this facilitates variations leading to large diversity among plants. Because of cross pollination higher yielding and disease resistant varieties are produced which serves the food need of human. A major byproduct of this plant animal interaction is honey produced by honey bees. Honey has been used since ancient civilization as a food additive and as medicine.

Our understanding of plant kingdom has changed over time because of the following reasons:

1. In the two-kingdom classification, plant kingdom included bacteria, cyanobacteria (blue-green algae), fungi, algae, bryophytes, pteridophytes, gymnosperms and angiosperms.
2. Later bacteria and cyanobacteria are removed to kingdom Monera, as they are prokaryotes.
3. Fungi are heterotrophs, with a cell wall of chitin; so they are also removed to kingdom Fungi.
4. Now the plant kingdom includes algae, bryophytes, pteridophytes, gymnosperms and angiosperms.

The gametophytes bear male sex organs called antheridia and female sex organs called archegonia. Antheridium is sessile and surrounded by a single-layered jacket. Archegonium is flask-shaped. It is partially embedded in the gametophyte.

The thallus structure in Rhodophyceae varies from unicellular to pseudoparenchymatous thallus.

1. Unicellular thallus (Porphyridium).
2. Filamentous thallus (Polysiphonia).
3. Pseudoparenchymatous thallus (Gelidium).

Phycocolloids are the water-holding colloidal substances, present on the surface of certain algae. e.g., Algin-Phaeophyceae, Carrageen-Rhodophyceae.

Vascular tissues, i.e., xylem and phloem are absent in bryophytes. The conduction of water and food takes place from cell to cell by diffusion.

1. The variation in colour is due to the quantity of the xanthophyll pigment, fucoxanthin.
2. Laminaria, Sargassum, Ectocarpus, Fucus, Dictyota.

S.No.	Sporophyte of Gymnosperms	Sporophyte of Bryophytes
(a)	It is the dominant phase; the plant has independent existence.	It is dependent on the gametophyte.
(b)	Vascular tissues are present.	Vascular tissues are absent.
(c)	The sporophyte is heterosporous and produces one megaspores and microspores.	The sporophyte is homosporous and produces only kind of spores.
(d)	Seeds are formed.	No seed is formed.

1. Ferns are homosporous and hence produce only one kind of spores.
2. Each spore germinates into a prothallus, the gametophytic stage.
3. The male and female sex organs, antheridia and archegonia, are borne on the same prothallus and hence fern prothallus is monoecious.

S.No.	Gametophyte of Bryophytes	Gametophyte of Pteridophytes
(a)	Gametophyte is the dominant phase in the life cycle.	It is a short-lived phase, represented by the prothallus.
(b)	Gametophyte supports the sporophyte throughout.	Gametophyte supports the sporophyte only in the initial stages.

The vascular plants dominated land due to the following features:

1. Presence of deep, penetrating and widespread roots which anchor the plants and also absorb water and minerals.
2. Covering of aerial parts with waterproof material like cutin.
3. Mechanical tissues are present to allow them to rise to great heights.

Pollen grains are deposited on the stigma of gynoecuim. Because of hydration pollen grains germinate by forming a pollen tube. The pollen tube penetrates the gynoecium and traverses down to reach the ovum.

1. Frond is a leaf-like the organ meant for performing photosynthesis process.
2. The cell wall in green algae is made up of cellulose (inner layer) and pectose (outer layer).

Selaginella shows seed habits because of:

1. Heterospory.
2. Formation of two types of gametophytes, male and female.
3. Only one megaspore mother cell is functional.

1. Chlorella.
2. Algin.
3. Frond.
4. Holdfast.

S.No.	Green Algae	Red Algae
(a)	They have characteristic pigments chlorophyll-a, chlorophyll-b, xanthophylls and carotene.	They have characteristic pigments, r-phycoerythrin, chlorophyll-a and chlorophyll-d.
(b)	The reserve food materials are in the form of pyrenoids(starch + proteins) and oil droplets.	The reserve food materials are in the form of floridean starch (amylopectin.
(c)	Phycocolloids are absent.	Phycocolloids are present.
(d)	They live in moderate depths and on the surface.	They live in very deep marine waters.

Differences between cytotaxonomy and chemotaxonomy are:

S. No.	Cytotaxonomy	Chemotaxonomy
(i)	It is based on cellular characteristics.	It is based on chemical constituents.
(ii)	It is related to genetic similarities and changes.	It is related to expression of and changes genetic similarities and changes.

The pteridophytes are restricted to narrow geographical regions because:

1. The gametophytes require cool, damp, shady places to grow.
2. They require water for fertilisation.

S.No.	Female Gametophyte of Angiosperms	Female Gametophyte of Gymnosperms
(a)	It has only seven cells.	It is multicellular and has more than seven cells.
(b)	Archegonia are absent.	Archegonia are present.
(c)	Only one female gamete is present.	Each archegonium has a female gamete.
(d)	Cells of gametophyte do not serve for nutrition of embryo.	Cells of gametophyte serve for nutrition of the embryo, serving as endosperm.
(e)	There is double fertilisation.	Double fertilisation is absent.

The artificial system of classification was mainly based on vegetative characters or on the androecium structure (system given by Linnaeus). Such system separated the closely related species since they were based on a few characteristics. The artificial system gives equal weightage to vegetative and sexual characteristics. This is not convincing because the vegetative characters are more easily affected by the environment.

Disadvantages of artificial system are given below:

1. This system uses only few superficial characters (i.e., habits, numbers, colours and shapes of leaves, etc.) which leads to many organisms grouped together.
2. They considered mainly the vegetative characters or the androecium characters as given by Linnaeus.

S.No.	Thallophytes	Bryophytes
(a)	They are all aquatic, freshwater or marine.	They are land plants, living in damp and shady places.
(b)	Sex organs are unicellular and do not have a protective covering.	Sex organs are multicellular and have a protective covering.
(c)	Zygote does not develop into an embryo; sporophyte is absent and zygote is the only diploid phase.	Zygote develops into an embryo and then into a diploid sporophyte.
(d)	Zygote undergoes meiosis during its germination.	Meiosis occurs in the spore mother cells during spore formation.

External features of monocotyledons:

1. Fibrous root system.
2. Single cotyledon in seeds.
3. Parallel venation in leaves.
4. Trimerous flowers.

Angiosperms are divided into two subgroups, i.e., dicotyledons and monocotyledons. This grouping is based on number of embryonic leaves or cotyledons. The two are commonly called as monocots and dicots.

Kingdom-Plantae includes multicellular eukaryotic organisms with photosynthetic mode of nutrition, cell wall with cellulose and plastids containing starch as the main reserve food.

Cycas resembles bryophytes and pteridophyte in following ways:

1. In its female gametophyte, archegonia are differentiated which contain the female gametes.
2. It has ciliated antherozoids.

Bryophytes show alternation of generation. The main plant body is gametophyte. After fertilisation of egg and spermatozoids, zygotes do not undergo reduction division and they produce a multicellular body called sporophyte. Then some cells undergo division and produce haploid spores which germinate to produce gametophyte.

1. Gemmae are the specialised structures formed for vegetative reproduction in liverworts.
2. They are multicellular, green, asexual buds that develop in small receptacles, called gemma cups, located on the dorsal surface of the thallus.
3. The gemmae become detached from the parent thallus and germinate into new thalli.

1. Selaginella and Salvinia are heterosporous.
2. They are called so, because they produce two types of spores, i.e. microspores and megaspores.

1. Cytotaxonomy: Cytotaxonomy is the system of classification based on cytological information like chromosome number, structure and their behaviour, especially during meiosis.
2. Chemotaxonomy: Chemotaxonomy is the system of classification that is based on the chemical constituents of the plants.

S.No.	Haplontic Life cycle	Diplontic Life cycle
(a)	The haploid phase is dominant and the diploid phase is represented only by the zygote.	The diploid phase is dominant and single-celled or few celled gametophytes are the only haploid phase in the life cycle.
(b)	Zygote undergoes meiosis; embryo and sporophyte are absent, e.g. Algae such as Spirogyra.	Zygote develops into an embryo and then into a sporophytic plant, e.g. Gymnosperms and angiosperms.