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Describe 2 principles (rules) to be followed when constructing a dichotomous key
Each couplet must be contrasting so that one fits the
situation at hand while the other does not
The key should have enough steps to identify each member
of the group
The number of steps in the key is one less than the number
of specimens
Briefly outline 3 mechanisms by which the chlorophyta maintain their genetic variability
Zygotic Meiosis: Found in some green algae, where the diploid zygote undergoes meiosis to produce haploid cells, contributing to genetic diversity.
Sporic Meiosis: Involves the formation of spores that undergo meiosis, contributing to variation in the next generation.
Gametic Meiosis: Involves the production of gametes (haploid cells), leading to sexual reproduction and genetic recombination.
Using named examples, describe the various types of life cycles seen in the algae
[Zygotic Meiosis ]
Mature, dominant adult organism is a haploid
individual which produces gametes by mitosis
These haploid gametes combine to form a diploid
zygote.
Zygote divides immediately by meiosis to form 4
haploid cells.
The zygote may develop into a zygospore to ‘ride out’
unfavourable environmental conditions, then divide into
the haploid cells when normal conditions return
EXAMPLES : Chlamydomonas, Volvox,
Spirogyra
Using named examples, describe the various types of life cycles seen in the algae
[Gametic Meiosis ]
Mature, dominant adult is a diploid individual
Diploid individual undergoes meiosis giving haploid gametes.
Each pair of haploid gametes combine to form a
diploid zygote.
Zygote develops into the diploid individual.
Since gametes are produced by meiosis → gametic meiosis.
aka. the diplontic diploid life cycle
the dominant adult individual in the life cycle is diploid
e.g Acetabularia
Using named examples, describe the various types of life cycles seen in algae [Sporic Meiosis]
The mature adult may exist either as a haploid gametophyte or as
a diploid sporophyte
▪ The gametophyte produces the gametes → 2 haploid gametes combine to
form a diploid zygote → Zygote divides to produce a sporophyte (an
autotroph which produces spores)
▪ The sporophyte produces haploid spores within sporogenous tissue via
meiosis.
▪ since meiosis gives rise to spores = sporic meiosis.
▪ The spores then develop by mitosis into multicellular haploid individuals (new gametophytes)
aka. the haplodiplontic cycle or the Haploid-Diploid life cycle:
▪ There are two types of generations, the one haploid and the other diploid,
within the life cycle of the species
e.g: Ulva
List 4 descriptive features of the bryophytes and tabulate the similarities and differerences with the green algae
- Epidermal layer with poorly
developed cutin-like substance - Pigmentation: chls. a, b &
carotenoids - Starch stored in chloroplasts
- These plants show alternation of
generations with the gametophyte
(n) dominating the life cycle
Similarities with algae:
Reproduction depends on free water
Flagellated reproductive cells,
The “amphibians of plant kingdom”
Water and mineral absorption directly
through thallus
DIFFERENCES: Bryophyta terrestrial, chlorophyta is not
Bryophyta are embryophytes but chlorophyta is not
Describe 4 characteristics that can be used to differentiate between bryophytes and polypodiophytes
Bryophytes:
1. The main plant body is a
haploid gametophyte.
2. Cuticle very poorly
developed.
3. True roots and leaves are
absent.
4. Vascular tissue is absent.
Pteridophytes:
1. Main plant body is a
diploid sporophyte.
2. Cuticle is well developed,
covering epidermis.
3. True roots and leaves are
present.
4. Vascular tissue is present.
Select 4 distinct characteristics of polypodiophytes and explain how each
characteristic has contributed to their adaptation to specific aspects of the terrestrial
environment
The water-conducting tissue (xylem)
– roots (water absorption),
– leaves (photosynthesis), and
– stems (structural support)
Explain why bryophytes are limited to life within habitats with appreciable amounts of water
lack of cuticle
– lack of developed conducting tissue (xylem & phloem)
They also require water for reproduction
Gymnosperms have more successfully colonized the land environment than
pteridophytes. BRIEFLY DESCRIBE five (5) gymnosperm characteristics that make them netter adapted than Pteridophytes
development of tap root system
- development of thick cuticle, etc.
- all have megaphylls
- upright thickened stem: vascular and cork cambia produce secondary growth
Instead of spores being dispersal units (as in bryophytes & pteridophytes), seeds are
dispersed (more effective as they can directly form new sporophyte plant)
No free water required for sperm transfer in gymnosperms
- male spore/gametophyte is a POLLEN grain, which carries male gamete/sperm to
egg (pollination and pollen tube)
Pinus and Cycas are common representatives of two different gymnosperm phyla.
Compare the morphology of Cycas and Pinus with regard to their stems, branches and
leaves. (5 marks]
Comparison of Morphology: Cycas vs. Pinus
Stems:
Cycas: Unbranched, columnar stem with a crown of leaves at the top.
Pinus: Branched stem with a pyramidal or conical shape.
Branches:
Cycas: No true branching; stem remains unbranched or rarely dichotomous.
Pinus: Regularly branched; has both long and dwarf shoots.
Leaves:
Cycas: Large, pinnate, compound leaves resembling palm leaves.
Pinus: Needle-like, simple leaves arranged in clusters (fascicles).
The seed was a major development among the spermatophytes. Provide TWO (2)
reasons why the seed was advantageous to their survival in terrestrial habitats. (2
marks]
Seed Habit = how a plant benefits by producing and dispersing seeds rather than dispersing spores
• contains new sporophyte individual = embryo: already started growth; individual doesn’t have
to develop from single cell (as in a spore)
• has a supply of food
• has a protective coating
• has a dispersal mechanism (by itself or in fruit if angiosperm)
• is resilient to extreme environmental conditions
• in most species to:
• very dry
• very hot or cold
• high pressure
