Class 11 Biology – Gymnosperms Notes
Complete notes on Gymnosperms, their general characteristics, differences from Angiosperms, Pinus, distribution in Nepal, xerophytic characteristics and economic importance.
Gymnosperms
Gymnosperms are plants whose seeds are unprotected. The term is derived from the Greek words gymnos, meaning naked, and sperma, meaning seed.
In gymnosperms, the ovules and the seeds developing from those ovules are not enclosed within a fruit wall. In other words, the ovary is absent.
According to the notes, gymnosperms are among the most ancient seed plants and originated during the late Palaeozoic era.
Gymnosperms are mostly evergreen plants, although a few deciduous forms are also found.
Their leaves may be large and fern-like or comparatively small and simple.
General Characteristics of Gymnosperms
- They are described in the handwritten notes as flowering plants, but they do not bear true flowers like those of angiosperms.
- They are naked-seeded plants; their seeds are not enclosed within fruits.
- They are cosmopolitan in distribution and are mainly found in xerophytic habitats.
- The main plant body is the sporophyte.
- The sporophyte is differentiated into roots, stem and leaves.
- Most gymnosperms are evergreen plants.
- The male reproductive structure is called the male cone.
- The female reproductive structure is called the female cone.
- Sexual reproduction is of an advanced oogamous type.
- Examples mentioned in the notes include Pinus and Cycas.
Difference Between Gymnosperms and Angiosperms
| Gymnosperms | Angiosperms |
|---|---|
| Gymnosperms are generally not herbaceous. | The majority of angiosperms are herbaceous. |
| They are terrestrial. | They may be aquatic or terrestrial. |
| They show xerophytic habitat. | They may or may not show xerophytic habitat. |
| Both scale leaves and foliage leaves are present. | Leaves are described in the source notes as being of one type. |
| The ovules are naked. | The ovules are protected by carpels. |
| Seeds are described in the source notes as endospermic. | Seeds may or may not be endospermic. |
Pinus
Systematic Position
General Description
Pinus is commonly called pine.
It is a tall evergreen tree and may sometimes attain a height of about 30 metres.
The main plant body represents the sporophyte and is differentiated into roots, stem and leaves.
Root of Pinus
The root system of Pinus is a tap root system.
The main root penetrates deeply into the soil and bears numerous lateral roots.
In many species, fungal hyphae grow symbiotically in association with the roots of Pinus.
Such associated roots are known as mycorrhizal roots.
According to the notes, mycorrhizal roots help increase or accumulate the phosphate content of the soil.
Stem of Pinus
The stem forms the main tree trunk of Pinus. It is woody in nature.
The main stem bears numerous branches. The notes describe the branches as being of two types:
1. Long Shoots
These form the normal main branches and continue their growth.
2. Dwarf Shoots
Dwarf shoots are smaller branches associated with the long shoots and bear foliage leaves.
Leaves of Pinus
The leaves of Pinus are of two types:
- Scale leaves
- Foliage leaves
1. Scale Leaves
Scale leaves are small, flat and brown-coloured.
They develop at the base of the foliage leaves.
The main function of the scale leaves is protection.
2. Foliage Leaves
Foliage leaves are green leaves that develop from the tips of dwarf shoots.
Their surface area is highly reduced and the leaves become greatly elongated.
Such elongated foliage leaves are commonly called needles.
Distribution of Pinus in Nepal
The handwritten notes list the following common species of Pinus occurring in Nepal and the Himalayan region.
1. Pinus roxburghii
It is commonly known as Chir pine.
The notes also mention local names such as Khote Sallo. It is described as abundant.
2. Pinus wallichiana
It forms pure or mixed forests on hill slopes.
According to the notes, it occurs at elevations ranging approximately from 6,000 to 11,000 feet above sea level.
3. Pinus gerardiana
It grows in the north-western Himalayas.
The notes place its occurrence roughly between 5,000 and 12,000 feet above sea level.
4. Pinus insularis
It is also known as Khasi pine.
It grows in the hills of the Eastern Himalayas.
5. Pinus merkusii
It occurs in the Eastern Himalayas.
Its dwarf shoot bears two needles.
6. Pinus armandii
It possesses five needles per dwarf shoot.
The notes describe it as a Chinese species.
Xerophytic Characteristics of Pinus
Pinus possesses several characteristics that help it survive where moisture availability is comparatively low.
- It commonly grows in habitats where there is limited availability of moisture.
- The leaves are reduced and modified into needles. This reduces the surface area available for transpiration.
- The leaves possess sunken stomata, which help reduce the rate of transpiration.
- The root system is highly developed and helps in the absorption of water.
Economic Importance of Gymnosperms
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Ornamental Plants
Several gymnosperms are cultivated in gardens for ornamental purposes. Examples mentioned in the notes include Cycas revoluta, Thuja and Araucaria.
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Timber
Wood obtained from gymnosperms such as Pinus and Cedrus is used for making furniture, matchboxes and building materials.
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Edible Seeds
The seeds of several cycads and conifers are used as food.
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Medicinal Importance
Ephedra yields the alkaloid ephedrine.
The notes state that ephedrine is used in medicines for the treatment of cough, asthma and bronchitis.
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Resins and Turpentine
Several gymnosperms provide commercially useful resins and turpentine.
Examples mentioned in the notes include Pinus, Abies balsamea, Tsuga canadensis and Agathis australis.
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Essential Oils
Some gymnosperm plants yield essential oils that are used for hygienic purposes and in perfumery.
Quick Revision
- Gymnosperms are naked-seeded plants.
- Their ovules and seeds are not enclosed within a fruit wall.
- The ovary is absent.
- Gymnosperms are mostly evergreen.
- The dominant plant body is the sporophyte.
- The sporophyte is differentiated into roots, stem and leaves.
- Male reproductive structures are called male cones.
- Female reproductive structures are called female cones.
- Pinus is commonly called pine.
- Pinus has a tap root system.
- Roots may form a symbiotic association with fungi, producing mycorrhizal roots.
- The stem is woody.
- Branches are described as long shoots and dwarf shoots.
- Leaves are of two types: scale leaves and foliage leaves.
- Foliage leaves are elongated and needle-like.
- Needle-shaped leaves reduce the surface area for transpiration.
- Sunken stomata reduce water loss.
- Pinus roxburghii is commonly known as Chir pine.
- Pinus insularis is known as Khasi pine.
- Pinus merkusii has two needles per dwarf shoot according to the notes.
- Pinus armandii has five needles per dwarf shoot.
- Gymnosperms provide timber, medicines, resins, turpentine and essential oils.
- Ephedra is a source of ephedrine.
Important Questions
- What are gymnosperms?
- Why are gymnosperms called naked-seeded plants?
- Write the general characteristics of Gymnosperms.
- Differentiate between Gymnosperms and Angiosperms.
- Write the systematic position of Pinus.
- Describe the general habit of Pinus.
- Describe the root system of Pinus.
- What are mycorrhizal roots?
- Describe the stem of Pinus.
- Differentiate between long shoots and dwarf shoots.
- Describe the two types of leaves found in Pinus.
- What are needle leaves?
- Write the common species of Pinus distributed in Nepal.
- Write a short note on Pinus roxburghii.
- Write a short note on Pinus wallichiana.
- Write the xerophytic characteristics of Pinus.
- How do needle-shaped leaves help Pinus reduce water loss?
- What is the importance of sunken stomata in Pinus?
- Write the economic importance of Gymnosperms.
- Name some gymnosperms used as ornamental plants.
- Write the medicinal importance of Ephedra.
- Name some gymnosperms that provide resins and turpentine.
Discussion
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