📘 NEET Notes (Gymnosperm)
🌲 Gymnosperms – Introduction & General Features
- The term Gymnosperm means “naked seed.”
- Gymnosperms are primitive seed-bearing plants.
- Seeds are not enclosed in fruit; ovules are exposed on the surface of megasporophylls.
- Considered as a connecting link between Pteridophytes and Angiosperms.
- Plant body is a sporophyte.
- Plants are generally woody, perennial, evergreen and autotrophic.
- They occur mainly as trees and shrubs, herbs are absent.
- Gymnosperms form dominant vegetation in colder regions.
- Most are xerophytes; a few occur in tropical and subtropical regions.
- Life cycle shows alternation of generations with dominant sporophyte and reduced gametophyte.
- They are heterosporous – produce microspores (male) and megaspores (female).
🌲 Gymnosperms – Morphology (Root, Stem, Leaf, Wood)
🔹 Roots
- Roots in gymnosperms are typically taproots, penetrating deep into the soil and anchoring the tall trees firmly.
- In many conifers, roots form symbiotic associations with fungi, known as mycorrhiza (e.g., Pinus). This allows the plant to absorb minerals, especially phosphorus, efficiently from nutrient-poor soils.
- In Cycas, roots exhibit a unique modification into coralloid roots, which are irregularly swollen and coral-like in appearance.
- These roots harbor colonies of cyanobacteria (e.g., Nostoc, Anabaena).
- Their role is nitrogen fixation, enriching the soil and supplying the host plant with usable nitrogen compounds.
🔹 Stem
- Gymnosperm stems are predominantly woody, erect and perennial, reflecting their adaptation to form large, long-lived trees.
- They exhibit secondary growth, producing both wood (secondary xylem) and bark (secondary phloem).
- Stems can vary in habit:
- Unbranched (as in Cycas), giving a palm-like appearance.
- Branched (as in Pinus, Cedrus), producing conical tree forms that dominate alpine forests.
🔹 Leaves
- Two types of leaves are often distinguished:
- Scale leaves – small, dry, non-photosynthetic, mainly protective in function.
- Foliage leaves – green, photosynthetic, often well-adapted to harsh conditions.
- In Cycas: foliage leaves are large, pinnately compound, resembling palm leaves.
- In conifers like Pinus: foliage leaves are needle-like, often borne in clusters.
- These needles are highly xerophytic: thick cuticle, sunken stomata, and reduced surface area help resist desiccation and withstand extremes of temperature and wind.
- Leaves are usually evergreen, ensuring year-round photosynthesis and adaptation to cold environments where growing seasons are short.
🔹 Wood
- Gymnosperm wood is a key distinguishing feature:
- Xylem: consists almost entirely of tracheids, long cells that conduct water and provide support.
- Phloem: sieve cells are present, but companion cells are absent (unlike in angiosperms).
- Types of wood:
Wood of gymnosperms is as following types:
- (a) Manoxylic
- Soft wood.
- Vascular tissues with medullary rays.
- Commercially less important.
- Example: Cycas.
- (b) Polyxylic
- Wood with many persistent cambium rings and bundles (text split across lines in the PDF).
- Example: Cycas.
- (c) Pycnoxylic
- Compact wood, without or with narrow medullary rays.
- Described in the PDF as commercially more important.
- Example in the PDF: Pinus.
- (d) Monoxylic
- Wood with a single persistent cambium ring and bundles.
- Example: Pinus.
- Exception: In Gnetum, true xylem vessels are present, showing angiosperm-like features.
🌲 Gymnosperms – Life Cycle
🔹 Sporophyte and Spore Formation
- Main plant body is sporophytic (diploid).
- Sporophyte produces microspores (male) and megaspores (female).
- Microspores are formed inside microsporangia borne on microsporophylls.
- Megaspores are formed inside ovules borne on megasporophylls.
- Microspore mother cells undergo meiosis to produce haploid microspores.
- Megaspore mother cell undergoes meiosis to produce haploid megaspores (usually one functional).
🔹 Male Gametophyte (Microspore → Pollen Grain)
- Microspores germinate into male gametophytes.
- Development is endosporic (within the spore wall).
- Male gametophyte is highly reduced and represented by the pollen grain.
- Pollen grains are carried by wind (anemophily) to the ovules.
- In Pinus, pollen grains have air bladders (sacci) to aid wind dispersal.
🔹 Female Gametophyte (Megaspore → Prothallus)
- Functional megaspore germinates to form the female gametophyte.
- Female gametophyte is multicellular and endosporic (develops within the megaspore).
- Archegonia develop at the micropylar end of the gametophyte.
- Each archegonium has a neck canal cell and a single egg cell.
🔹 Pollination
- Pollination is by wind.
- Pollen grains are carried to the micropyle of the ovule.
- A pollen chamber is formed at the tip of nucellus, where pollen grains are received.
🔹 Fertilization
- Two types of fertilization in gymnosperms:
- Zoodiogamy:
- Seen in primitive gymnosperms like Cycas and Ginkgo.
- Male gametes are motile and multiflagellate.
- Require water for swimming to the egg.
- Siphonogamy:
- Seen in conifers (Pinus) and Gnetum.
- Male gametes are non-motile.
- Pollen tube carries gametes directly to the egg.
- Zoodiogamy:
- Fertilization results in the formation of zygote (2n).
🔹 Embryo and Seed Development
- Zygote develops into an embryo within the ovule.
- Embryo development often shows polyembryony:
- Multiple embryos may begin to form.
- Only one embryo matures in most cases.
- Endosperm in gymnosperms is haploid, formed from the female gametophyte before fertilization.
- Seeds are naked (not enclosed in fruit).
- Seed consists of:
- Protective seed coat.
- Stored haploid endosperm.
- Diploid embryo.
🔹 Alternation of Generations
- Alternation of generations is heteromorphic.
- Sporophyte is dominant, long-lived, and independent.
- Gametophyte is reduced and dependent (endosporic).
- Life cycle → clear progression from dominant sporophyte to reduced gametophyte.
🌲 Gymnosperms – Classification
🔹 Order: Cycadales (e.g., Cycas)
- Plants are palm-like in appearance.
- Stem is unbranched and manoxylic (soft wood with broad rays).
- Roots show coralloid structures containing cyanobacteria (Nostoc, Anabaena).
- Leaves are pinnately compound and circinate vernation is present (young leaves coiled).
- Plants are dioecious (male and female plants separate).
- Male cone is compact; female cones are loose or absent.
- Fertilization is zoodiogamous (motile, multiflagellate male gametes).
🔹 Order: Coniferales (e.g., Pinus, Cedrus, Cupressus, Taxus)
- Plants are tall trees forming coniferous forests in temperate and alpine regions.
- Stem is branched, wood is pycnoxylic (compact, narrow rays, commercially valuable).
- Leaves are needle-like, xerophytic, evergreen.
- Plants are usually monoecious (male and female cones on same plant).
- Male cones are small and short-lived; female cones are large and persistent.
- Fertilization is siphonogamous (non-motile gametes carried by pollen tube).
🔹 Order: Ginkgoales (e.g., Ginkgo biloba)
- Known as a living fossil (only one living species).
- Tree with fan-shaped leaves, dichotomous venation.
- Plant is dioecious.
- Fertilization is zoodiogamous (motile gametes).
- Seeds have a fleshy outer covering.
🔹 Order: Gnetales (e.g., Gnetum, Ephedra, Welwitschia)
- Unique among gymnosperms → show some angiosperm-like characters.
- Presence of true vessels in xylem (exception among gymnosperms).
- Leaves are broad and show reticulate venation in Gnetum.
- Plants may be shrubs, climbers (Gnetum), or small trees (Ephedra).
- Reproduction is by siphonogamy.
- Seeds resemble angiosperm ovules in some respects.
🌲 Gymnosperms – Special Features & Economic Importance
🔹 Special Features
- Gymnosperms bear naked seeds (not enclosed in fruits).
- They are heterosporous (produce both microspores and megaspores).
- Gametophytes are endosporic (develop within spores).
- Fertilization may be by:
- Zoodiogamy → motile male gametes (in Cycas, Ginkgo).
- Siphonogamy → non-motile gametes carried by pollen tube (in conifers, Gnetum).
- Endosperm is haploid, formed before fertilization (female gametophyte).
- Polyembryony is often observed during embryo development.
- Gymnosperms are considered an intermediate group between pteridophytes and angiosperms, showing evolutionary advancement.
🔹 Economic Importance
- Timber: Conifers (Pinus, Cedrus, Picea) provide softwood widely used in construction, paper, and furniture.
- Resins and Oils:
- Pinus yields turpentine (resin) and wood oil.
- Cedrus deodara yields valuable deodar wood.
- Medicinal:
- Ephedra → source of the alkaloid ephedrine (used in asthma treatment).
- Taxus → yields taxol, an anti-cancer drug.
- Food:
- Seeds of Cycas and Pinus gerardiana (chilgoza) are edible.
- Ginkgo seeds also used in traditional medicine.
- Ornamental:
- Cycas, Thuja, Araucaria used as garden plants.
- Fossils: Gymnosperm fossils (like Williamsonia) provide insight into plant evolution.
Practice Questions
Q1. Assertion (A): Gymnosperms are called “naked seed plants” because their ovules are not enclosed in ovaries.
Reason (R): In gymnosperms, carpels fuse to enclose the ovule and later form fruit.
(a) Both A and R are true, and R is the correct explanation of A
(b) Both A and R are true, but R is not the correct explanation of A
(c) A is true, but R is false
(d) Both A and R are false
Answer: (c)
Q2. Assertion (A): Secondary growth is a characteristic feature of gymnosperms.
Reason (R): Their vascular bundles are conjoint, collateral, open, with a persistent cambium.
(a) Both A and R are true, and R is the correct explanation of A
(b) Both A and R are true, but R is not the correct explanation of A
(c) A is true, but R is false
(d) Both A and R are false
Answer: (a)
Q3. Assertion (A): Coralloid roots of Cycas harbour nitrogen-fixing cyanobacteria.
Reason (R): The cyanobacteria fix nitrogen and provide it to the host plant.
(a) Both A and R are true, and R is the correct explanation of A
(b) Both A and R are true, but R is not the correct explanation of A
(c) A is true, but R is false
(d) Both A and R are false
Answer: (a)
Q4. Assertion (A): Mycorrhizal associations occur in gymnosperms such as Pinus.
Reason (R): Fungal hyphae increase the surface area of roots for mineral absorption.
(a) Both A and R are true, and R is the correct explanation of A
(b) Both A and R are true, but R is not the correct explanation of A
(c) A is true, but R is false
(d) Both A and R are false
Answer: (a)
Q5. Assertion (A): Gymnosperm leaves are needle-like, with thick cuticle and sunken stomata.
Reason (R): These xeromorphic features reduce water loss and help survival in extreme climates.
(a) Both A and R are true, and R is the correct explanation of A
(b) Both A and R are true, but R is not the correct explanation of A
(c) A is true, but R is false
(d) Both A and R are false
Answer: (a)
Q6. Assertion (A): All gymnosperms are dioecious, bearing male and female cones on different plants.
Reason (R): Pinus is an exception, being monoecious with both male and female cones on the same plant.
(a) Both A and R are true, and R is the correct explanation of A
(b) Both A and R are true, but R is not the correct explanation of A
(c) A is true, but R is false
(d) Both A and R are false
Answer: (c)
Q7. Assertion (A): Gametophytes of gymnosperms are free-living and photosynthetic like bryophytes.
Reason (R): Gametophytes in gymnosperms are highly reduced and remain dependent, developing within the sporangia of the sporophyte.
(a) Both A and R are true, and R is the correct explanation of A
(b) Both A and R are true, but R is not the correct explanation of A
(c) A is true, but R is false
(d) Both A and R are false
Answer: (c)
Q8. Assertion (A): Fertilization in gymnosperms does not require external water.
Reason (R): Male gametes are carried to the egg by a pollen tube during siphonogamy.
(a) Both A and R are true, and R is the correct explanation of A
(b) Both A and R are true, but R is not the correct explanation of A
(c) A is true, but R is false
(d) Both A and R are false
Answer: (a)
Q9. Assertion (A): In lower gymnosperms like Cycas, fertilization is siphonogamous.
Reason (R): Male gametes in Cycas are motile and multiciliate, swimming to reach the egg.
(a) Both A and R are true, and R is the correct explanation of A
(b) Both A and R are true, but R is not the correct explanation of A
(c) A is true, but R is false
(d) Both A and R are false
Answer: (d)
Q10. Assertion (A): The endosperm of gymnosperms is haploid.
Reason (R): It develops before fertilization from the female gametophyte.
(a) Both A and R are true, and R is the correct explanation of A
(b) Both A and R are true, but R is not the correct explanation of A
(c) A is true, but R is false
(d) Both A and R are false
Answer: (a)
Q11. Which of the following statements are correct regarding gymnosperms?
(i) Ovules are exposed and borne on megasporophylls without any ovary wall.
(ii) Male gametophyte is free-living and photosynthetic.
(iii) Pollination is usually by insects.
(iv) Fertilization occurs without the need for external water.
(a) Only (i) and (iv)
(b) Only (i) and (iii)
(c) Only (ii) and (iv)
(d) (i), (ii) and (iii)
Answer: (a)
Q12. Which of the following features belong to Cycas?
(i) Ovules are orthotropous and very large.
(ii) Wood is manoxylic, with abundant parenchyma.
(iii) Fertilization occurs by motile, multiciliate sperm.
(iv) Seeds are enclosed within fruits.
(a) (i), (ii), and (iii)
(b) (ii), (iii), and (iv)
(c) (i) and (iv) only
(d) All four are correct
Answer: (a)
Q13. Which of the following statements are correct about the gymnosperm endosperm?
(i) It is diploid, developing after fertilization.
(ii) It is haploid, formed before fertilization.
(iii) It nourishes the developing embryo inside the seed.
(iv) It is derived from the male gametophyte.
(a) (i) and (iii)
(b) (ii) and (iii)
(c) (i) and (iv)
(d) (ii) and (iv)
Answer: (b)
Q14. Which of the following statements correctly describe Pinus?
(i) Leaves are needle-like, with sunken stomata and thick cuticle.
(ii) Pollen grains are winged, adapted for wind pollination.
(iii) Male and female cones occur on separate plants (dioecious).
(iv) Resin ducts are present in the wood.
(a) (i), (ii), and (iv)
(b) (i), (iii), and (iv)
(c) Only (ii) and (iii)
(d) All four are correct
Answer: (a)
Q15. Which of the following are features of Gnetales?
(i) Presence of vessels in xylem.
(ii) Double fertilization, but without triploid endosperm.
(iii) Net-veined leaves in some species.
(iv) Seeds enclosed within carpels.
(a) (i), (ii), and (iii)
(b) (i), (iii), and (iv)
(c) (ii), (iii), and (iv)
(d) All four
Answer: (a)
Q16. Which statements are true about polyembryony in gymnosperms?
(i) It occurs due to fertilization of multiple archegonia (simple polyembryony).
(ii) It can also occur due to cleavage of a single zygote (cleavage polyembryony).
(iii) All embryos survive and develop into multiple sporophytes.
(iv) Usually only one embryo survives to maturity.
(a) (i), (ii), and (iv)
(b) (i) and (iii)
(c) (ii) and (iii)
(d) All four are correct
Answer: (a)
Q17. Which of the following statements are correct regarding Ginkgo biloba?
(i) It is dioecious, with separate male and female plants.
(ii) Male gametes are motile, multiflagellate sperm.
(iii) The wood is manoxylic with abundant parenchyma.
(iv) It is the only surviving member of Ginkgoales.
(a) (i), (ii), and (iv)
(b) (ii) and (iii)
(c) (i), (iii), and (iv)
(d) All four are correct
Answer: (a)
Q18. Which features distinguish gymnosperm wood?
(i) It is pycnoxylic in conifers, dense with narrow medullary rays.
(ii) Manoxylic wood of Cycas contains more parenchyma.
(iii) Vessels are absent in most gymnosperms.
(iv) Resin canals are absent in gymnosperm wood.
(a) (i), (ii), and (iii)
(b) (i) and (iv)
(c) (ii), (iii), and (iv)
(d) All four are correct
Answer: (a)
Q19. Which of the following correctly describe the reproduction in gymnosperms?
(i) Pollination is usually by wind.
(ii) Fertilization is siphonogamous in conifers.
(iii) Archegonia are absent in gymnosperms.
(iv) Seeds develop after fertilization but remain naked.
(a) (i), (ii), and (iv)
(b) (i) and (iii)
(c) (ii) and (iii)
(d) All four are correct
Answer: (a)
Q20. Which of the following statements are correct regarding Cycas and ferns?
(i) Both show circinate vernation in young leaves.
(ii) Both have manoxylic wood with abundant xylem parenchyma.
(iii) Both exhibit archegonia and antheridia as reproductive organs.
(iv) Both show seeds enclosed in ovary.
(a) (i) and (iii)
(b) (ii) and (iv)
(c) (i), (ii), and (iii)
(d) All four are correct
Answer: (a)
Q21. Although gymnosperms produce seeds, they are called “naked seed plants.” Which feature best explains this?
(a) Ovules and seeds remain exposed on the surface of megasporophylls without enclosing carpels
(b) Their ovules are enclosed within ovaries, but fruits fail to develop
(c) They produce seeds without fertilization
(d) Their seeds are sterile and non-functional
Answer: (a)
Q22. In Cycas, the large ovules are directly visible to the naked eye. Which structural feature makes them unique among gymnosperms?
(a) Ovules are orthotropous, unitegmic, and surrounded by three distinct integumentary layers
(b) Ovules are anatropous, bitegmic, and enclosed in carpels
(c) Ovules are reduced, minute, and embedded inside strobili
(d) Ovules are protected by a fleshy fruit wall
Answer: (a)
Q23. Why is fertilization in gymnosperms considered more advanced than that of pteridophytes but less advanced than angiosperms?
(a) It requires free water for motile sperm like pteridophytes
(b) It is siphonogamous in most groups, eliminating the need for external water, but ovules remain exposed unlike in angiosperms
(c) Double fertilization occurs with triploid endosperm as in angiosperms
(d) Male gametophytes are free-living and photosynthetic
Answer: (b)
Q24. In conifers like Pinus, fertilization is delayed by nearly a year after pollination. What explains this unusual delay?
(a) Archegonia take months to differentiate after pollination, and pollen tube growth is extremely slow through nucellar tissue
(b) Seeds must mature fully before fertilization can occur
(c) Male gametophyte fails to germinate immediately due to dormancy
(d) Fertilization requires external rainwater to activate sperm
Answer: (a)
Q25. In gymnosperms, polyembryony is common. Which statement best reflects its evolutionary consequence?
(a) All embryos mature and give rise to multiple sporophytes per seed
(b) Usually only one embryo survives, but polyembryony provides a survival advantage by increasing chances of successful sporophyte formation
(c) It results in haploid sporophytes developing from gametophyte tissue
(d) It allows direct formation of sporophytes without fertilization
Answer: (b)
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