Test: Gymnosperms (NCERT) - NEET MCQ

A mycorrhiza is a symbiotic association of a fungus with a root system. The mycorrhizal roots of Pinus occur near the soil surface. They are devoid of root hair and root cap. The fungus commonly associated with mycorhizic roots of Pinus is Boletus elegans.

The correct pattern of arrangement of reproductive structures for gymnosperms is:

Spores → Sporangia → Sporophylls → Strobili.
Spores are produced in the Sporangia, which are located on the Sporophylls, and these are arranged in Strobili (cones), which is the main reproductive structure of gymnosperms.

More Explanation on this:
Spores
In gymnosperms, spores are the first stage in the reproductive cycle. These are single-celled reproductive units that can develop into a new organism without the need for fertilization. Gymnosperms produce two types of spores: microspores and megaspores.

Sporangia
The spores are contained within structures called sporangia. Sporangia are specialized for spore production and are typically found on the undersides of leaves or within cones in gymnosperms. Each sporangium can produce numerous spores.

Sporophylls
Sporophylls are specialized leaves that bear sporangia. In gymnosperms, sporophylls are usually arranged in a cone-like structure. Depending on the type of spore they produce, sporophylls can be either microsporophylls (bearing microsporangia and producing microspores) or megasporophylls (bearing megasporangia and producing megaspores).

Strobili (Cones)
Strobili, or cones, are the reproductive structures of gymnosperms where sporophylls are found. There are male cones that contain microsporophylls and female cones that contain megasporophylls. The male cones release pollen (containing the male gametophyte), which is carried by the wind to the female cones, leading to fertilization and the production of seeds.

Pinus and Cedrus have branched stem. The main stem shows monopodial branching. Stem branches are of two types, long and dwarf. The dwarf branches possess 1-5 needle-like follage leaves Which are surrounded at the base by a sheath of scale leaves.

The correct answer is:

Option 4: Cedrus

Explanation: In Cedrus (a gymnosperm), the male and female gametophytes do not have a free-living independent existence. Instead, they are dependent on the sporophyte for nourishment and protection. In contrast, in Pteris (a fern), Funaria (a moss), and Polytrichum (another moss), the gametophytes are free-living and independent.

Correct answer:. A, B, D

Explanation:

• Statement A is correct: In Pinus, male and female cones are typically borne on the same tree (monoecious).
• Statement B is correct: In Cycas, male cones and megasporophylls (female cones) are borne on different trees (dioecious).
• Statement C is incorrect: The stem of Cycas is unbranched, while the stems of Pinus and Cedrus can be branched.
• Statement D is correct: Gymnosperms generally have tap roots.

Correct answer: 3 and 4

Explanation:

• Statement 1 is incorrect: Gymnosperms are heterosporous, they produce haploid microspores and megaspores.
• Statement 2 is incorrect: The reduced male gametophyte is called a pollen grain, not the microsporangia.

The specific term "mycorrhizal roots" would more accurately describe the symbiotic relationship rather than the physical form of the roots, and gymnosperms like Pinus generally start with a tap root system, which may not perfectly capture the essence of the mycorrhizal association but aligns more closely with the root structure potentially involved in such symbiosis.

The megaspore mother cell is differentiated from one of the cells of the nucellus. The nucellus is protected by envelopes and the composite structure is called an ovule. The ovules are borne on megasporophylls which may be clustered to form the female cones. The megaspore mother cell divides meiotically to form four megaspores. One of the megaspores enclosed within the megasporangium develops into a multicellular female gametophyte that bears two or more archegonia or female sex organs. The multicellular female gametophyte is also retained within megasporangium

In conifers, the needle-like leaves reduce the surface area. Their thick cuticle and sunken stomata also help to reduce water loss.

The pollen grain is released from the microsporangium. They are carried in air currents and come in contact with the opening of the ovules borne on megasporophylls. The pollen tube carrying the male gametes grows towards archegonia in the ovules and discharge their contents near the mouth of the archegonia. Following fertilisation, zygote develops into an embryo and the ovules into seeds. These seeds are not covered

The correct answer is: C: I, II, and III only

- I. Coralloid roots: Gymnosperm Cycas has coralloid roots that contain symbiotic cyanobacteria, aiding in nitrogen fixation.
- II. Unbranched stems: Cycas exhibits unbranched stems, which is a characteristic feature of this gymnosperm.
- III. Pinnate persistent leaves for a few years: Cycas has pinnate leaves that persist for several years, contributing to its distinct appearance.
- IV. Male cones and megasporophylls borne on the same plant: This option is incorrect as male and female reproductive structures are typically on separate Cycas plants.

the giant redwood tree Sequoia is one of the tallest tree species

Fig: Sequoia

Gymnosperms are characterized by seeds that are not enclosed by any ovary wall and remain exposed both before and after fertilization. This is in contrast to angiosperms where seeds are enclosed within a fruit.

Pollen grains develop in the microsporangia.

Unlike bryophytes and pteridophytes, in gymnosperms the male and the female gametophytes do not have an independent free-living existence. They remain within the sporangia retained on the sporophytes.