General Characteristics of Gymnosperms, Practice Problems and FAQs

Did you know that seeds can exist without fruits? When we think of seeds, we generally think of them as the hard structures that are found within fruits and are used to plant new trees. But, the fact is that only the seeds of flowering plants remain enclosed within fruits whereas the seeds of non-flowering plants do not. Such non-flowering plants bearing naked seeds belong to the division Gymnospermae and are commonly known as gymnosperms.

The word ‘Gymnosperm’ has been derived from two words, ‘gymnos’ meaning naked and ‘sperma’ meaning seeds. This is coherent with the feature of bearing naked seeds by the plants belonging to this division. The ovules remain exposed as they are not enclosed by the ovary wall before fertilisation, same is the case with seeds after fertilisation. Did you know that gymnosperms were the dominant plants on land around 200 years ago? Cool, right? Come let’s learn more about gymnosperms.

Table of contents

• General characteristics of gymnosperms
• Practise problems
• FAQs

General characteristics of gymnosperms

Gymnosperms are the first group of plants which are seeded. The seeds in gymnosperms are not enclosed within a fruit. They are vascular plants having the following tissue systems:

• Xylem: Helps in transportation of water
• Phloem: Helps in transportation of food

Habitat

They can survive in dry and cold habitats and are distributed worldwide. A vast majority of gymnosperms, especially the conifers, are predominant in the temperate and subarctic regions. Cycads and gnetophytes are mainly found in the tropical or subtropical regions.

Plant body of gymnosperms

The plant body of gymnosperms is differentiated into well-defined roots, shoots and leaves. They are woody perennials which include medium-sized trees or tall trees and shrubs.

                                         Fig: Some common gymnosperms

The main plant body of gymnosperms is a diploid sporophyte and is heterosporous in nature, that is, it produces two different types of spores - male microspores and female megaspores.

The spores are borne on chambers known as sporangia that are present on modified leaves known as sporophylls.

The haploid gametophytes are inconspicuous and depend on the sporophyte for nutrition and survival. The microspores develop into the male gametophyte known as pollen grain. The megaspore develops into a multicellular female gametophyte that bears two or more female sex organs or archegonia.

Roots

Gymnosperms have a taproot system. Their roots have several modifications depending on the organisms with which they are associated.

                                                 Fig: Tap root of Pinus

The roots of different gymnosperms form symbiotic associations with different organisms such as fungi and cyanobacteria.

Association with fungi: Mycorrhiza

The symbiotic association of the roots of gymnosperms with fungi is called mycorrhizae.The fungi helps to capture minerals such as organic nitrogen, phosphorus, iron and other nutrients by solubilising it. The fungal hyphae obtain nutrients beyond the root zone and make it available to the plants. Plants, in return, provide the sugars they produce by photosynthesis to the fungi as food. Thus heterotrophic fungi procure nutrition from the gymnosperm. This is a characteristic feature of Pinus roots.

                Fig: Symbiotic association of roots of Pinus with fungus

Association with nitrogen-fixing cyanobacteria

Cycads naturally grow in habitats like sand dunes and steep rocks wherein the nutrients are inaccessible. They have special root modifications that allow them to thrive in such challenging conditions. The roots of these plants possess symbiotic associations with cyanobacteria such as Nostoc or Anabaena and are called coralloid roots.

                                                   Fig: Coralloid roots in Cycas

These roots help in the fixation of atmospheric nitrogen into absorbable forms like ammonia.

                              GIF: Nostoc

Stem

Gymnosperms have an erect (straight) stem as the main axis of growth. Stem can be branched or unbranched.

• Unbranched columnar stem is seen in Cycas which is covered by twisted bands of persistent rhomboidal leaf bases.
• Branched stems are seen in Pinus, which may reach a height of 10-50 metres.

                                             Fig: Types of stems in gymnosperms

In conifers such as Pinus, the lower branches are longer than the upper branches which gives the tree its characteristic christmas tree like shape.

Leaves

Gymnosperms have two major types of leaves, i.e., scaly and foliage leaves.

                                                               Fig: Types of leaves

Scaly leaves

The scaly leaves are brown, thick, tough and needle-like leaves. These can be found developing in spiral rows. In Cycas, the scaly leaves alternate with the foliage leaves.

                                        Fig: Scaly leaves of Cycas

Foliage leaves

The foliage leaves are green, soft, large, pinnate and needle-like leaves. They are petiolate and usually have a broad base.

                                        Fig: Foliage leaves of Cycas

Foliage leaves can be of two types -

• Simple foliage leaves - The main leaf is complete and undivided in nature.

                         Fig: Simple foliage leaf of Gingko

• Compound foliage leaves - The main leaf is divided into smaller leaflets. These leaflets arise from either side of the stalk or rachis. These are more appropriately classified under pinnately compound foliage leaves.

                                     Fig: Pinnately compound foliage leaves

Adaptations of leaf

The leaves of gymnosperms are adapted to extreme conditions of temperature, humidity and wind. These adaptations have been discussed below -

Sporophylls

Sporophylls are modified leaves of gymnosperms which play a major role in reproduction. They contain numerous sporangia which produce spores, vital for reproduction. Sporophylls are usually compacted into a structure also known as strobili or cones.The male sporangia, also known as the microsporangia are borne on leaves called microsporophylls, which are clustered and compacted together to form the male strobili.The female sporangia, also known as the megasporangia are borne on leaves called megasporophylls, which are clustered and compacted together to form the female strobili.

                                       Fig: Strobili

Based on the presence of strobili in the gymnosperms, sporophytes can be of two types:

• Monoecious: Bisexual gymnosperms having both male and female strobili.
• Dioecious: Unisexual gymnosperms having either male or female strobili.

                    Fig: Monoecious and dioecious gymnosperms

Practice Problems

1. Which among the following is the correct statement?

1. All gymnosperms are homosporous
2. All gymnosperms are heterosporous
3. Mostly all gymnosperms are heterosporous and only few are homosporous
4. All gymnosperms and all pteridophytes are heterosporous

Solution: All gymnosperms and few pteridophytes are heterosporous as they produce two different kinds of spores. The two different kinds of spores are microspores and megaspores. Microspores develop into male gametophytes and megaspores develop into female gametophytes.

Thus, the correct option is b.

2. Which of the following is an adaptation in Pinus for reducing water loss by transpiration?

1. Sunken stomata
2. Thick cuticle
3. Needle like leaves
4. All of these

Solution: Pinus is a gymnosperm. The leaves in Pinus are well adapted to withstand harsh temperatures. Presence of sunken stomata, thick cuticle and needle-like leaves play an important role in reducing water loss. Sunken stomata remain deep seated in the epidermal layer and hence reduce transpiration. Cuticle is water-proof and hence thick cuticle helps to reduce water loss. The needle-like leaves reduce exposed surface area for water loss Thus, the correct option is d.

3. Symbiotic association in roots is found in

1. Cycas
2. Pinus
3. Both and b
4. Gingko

Solution: The roots of Pinus show fungal association. These roots are called mycorrhiza. Fungi help to absorb water and minerals like phosphorus for the plant and the plant, in turn, provides nourishment. This type of beneficial association is called mutualism or symbiosis.

The coralloid roots of Cycas show symbiotic association with cyanobacteria. The cyanobacteria help in nitrogen fixation whereas in return the Cycas provides a habitat for it to grow.

Thus, the correct option is c.

4. The similarity between gymnosperms and pteridophytes is that

1. They both produce seeds
2. They have vessels in xylem
3. have independent gametophytes
4. they possess archegonia

Solution: Gymnosperms resemble pteridophytes in having archegonia. Archegonia are the female sex organs which are present on the female gametophyte of both gymnosperms and pteridophytes.

Unlike gymnosperms, pteridophytes do not produce seeds. Vessels in xylem are found only in angiosperms. Pteridophytes have independent gametophytes but gymnosperms have a dependent and highly reduced gametophyte.

Thus, the correct option is d.

FAQs

1. Why are conifers the dominant flora of temperate regions?

Answer: Conifers are the dominant flora of the North temperate region because -

• They have many xerophytic adaptations like thick cuticle, needle-like leaves and sunken stomata to reduce the loss of water by transpiration.
• They are evergreen and shed their leaves throughout the year which helps them to survive in cold regions with distinct seasons.
• Due to their evergreen nature, they continue to prepare food throughout the year.
• They have enzymes that are functional even at -35^oC.

2. When did gymnosperms originate on planet Earth?

Answer: The gymnosperms originated during the late Paleozoic era and are the most ancient seed plants. However, they flourished well during the Mesozoic era.

3. Which is the tallest plant species?

Answer: The tallest tree in the world is called Hyperion (Sequoia sempervirens). It is the Coast Redwood and is 115.54m tall. It is located in the remote areas of Redwood National Park, California.

4. How are gymnosperms different from angiosperms?

Answer: Gymnosperms are the non-flowering plants which are the first seeds plants to have evolved on earth. They bear naked seeds that are not enclosed within fruits. Angiosperms are the flowering plants which bear seeds enclosed within fruits. They evolved a lot later when compared to gymnosperms but presently, angiosperms are the most dominant plant species on earth.

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