Plant Diversity

Question 1

What are the 4 major groups?

Answer 1

The plant kingdom has been classified into four major groups, the bryophytes, pterophytes, cone-bearing plants (gymnosperms)
and flowering plants (angiosperms)

Question 2

What are the criteria for classification?

Answer 2

by the presence or absence of:
* vascular tissue (xylem and phloem)
true leaves and roots
* dependence on water to reproduce
* seeds or spores
* cones or flowers
* fruit

Question 3

What do the classification characteristics tell us?

Answer 3

help give an understanding of the evolutionary changes that have taken place in terrestrial plants. The chart below shows a simple classification of terrestrial plants and also reflects the major stages of plant evolution.

Question 4

Explain what bryophytes are.

Answer 4

tiny terrestrial plants with no vascular tissue, true roots or leaves. They are poorly adapted to life on land and have to live in moist, shady places growing on rocks, trees and soil

Question 5

Give 3 examples of bryophytes.

Answer 5

mosses, liverworts and hornworts (Mosses and liverworts collectively are called bryophytes)

Question 6

Evolution of Bryophyta.

Answer 6

Bryophyta are believed to have evolved from
complex green algae that invaded land more than 400 million years ago. As such they are the simplest land plants.

Question 7

List and explain 8 characteristics of bryophytes.

Answer 7

1. have no vascular tissues and, therefore are unable to transport water and food around the plant.
   They absorb water through their entire surface. (Small moss plants)
2. have no true roots, stems or leaves. They have rhizoids, fine outgrowths of the ‘stem’, to anchor the plant.
3. have no cuticle, therefore have no means to prevent water loss.
4. have no strengthening tissues such as xylem, therefore can not grow tall.
5. are homosporous, ie their haploid spores are all the same size.
6. depend on water for fertilisation as their motile male gametes (sperm) have to swim to reach the female gamete (egg).
   have a life cycle with a well-defined alternation of generations:
7. the gametophyte (haploid) is the dominant generation. It is photosynthetic, therefore is free-living and it produces gametes.
8. the sporophyte (diploid) is attached to and dependent on the gametophyte generation. It produces haploid spores by meiosis. This is in contrast to the vascular plants, in which the dominant generation is the photosynthetic sporophyte.
   (Moss plants with attached sporophyte)

Question 8

What happens to dry bryophytes with water?

Answer 8

When it has been particularly dry the moss plants appears brownish and dead. However after a few minutes of being splashed with water the plants revive and become green again.

Question 9

What is a sign of bryophytes aquatic origin?

Answer 9

Although bryophytes have become adapted to life on land, an apparent sign of their aquatic origin is a motile (flagellated) sperm which depends on water to swim to the egg for fertilization.

Question 10

Give explanation for vascular plants.

Answer 10

plants have developed special
adaptations to enable them to cope in a dry environment, with these adaptations they are
grouped and are known as vascular plants.

Answer 11

To live successfully on land plants must have adaptations that:
* Prevent desiccation
The cuticle (a waxy layer of cutin covering the aerial parts of plants) and stomata help decrease water loss.

Answer 12

Aid nourishment,
To aid nourishment the development of the following was needed:
⁃ roots to absorb water and mineral salts from the soil, as well as to anchor the plant and store food.
⁃ vascular tissue, xylem and phloem to conduct water and minerals and the products of photosynthesis to various parts of plant. Hence the term, vascular plants.
⁃ vascular - has tubes that carry liquids (sap in plants or blood in animals)
⁃ supporting tissues, consisting largely of xylem, to hold up the leaves to get magine sunlight for photosynthesis.

Answer 13

Aid reproduction
The development of spores and seeds provide an effective means of reproducing.
⁃ Early land plants, bryophytes and pterophytes are seedless. They, like the algae, reproduce by means of spores (genetic copies of the parent plant).
Reproduction by spores is successful in a watery environment as the spores float away and grow elsewhere. However on land the spores are vulnerable to dangers such as drying out.
⁃ Later land plants, gymnosperms and
angiosperms, produced seeds. Further modifications of roots, stems and leaves have enabled the various species of vascular plants to survive in a variety of habitats and environmental conditions. The ability of vascular plants to do well in so many different habitats is the main reason they have become the dominant terrestrial group of plants.

Question 14

what are the main differences between nonvascular and vascular plants?

Answer 14

Vascular plants differ from the nonvascular bryophytes in that vascular plants:
* possess vascular tissue, i.e. xylem and phloem which forms a central column (stele) through the plant.
. the sporophyte phase is the larger and more conspicuous generation of the life cycle.

Question 15

How are vascular plants classified?

Answer 15

Seedless plants (lower vascular plants)
These reproduce by spores and are seedless, e.g. pterophytes or ferns.
* Seed-bearing plants (higher vascular plants)
These reproduce by seeds, e.g. cone-bearing plants (gymnosperms) and flowering plants (angiosperms).

Question 16

Define seedless plants using examples.

Answer 16

Pterophytes, e.g. ferns
The ferns are one group of the lower vascular plants; other groups include the whisk ferns, club mosses and horsetails. They all are seedless.

Question 17

Pterophytes evolution.

Answer 17

Pterophytes are more evolved for terrestrial life than bryohytes and are much larger than mosses, but most species are less than 1 metre tall. Tree ferns are taller however with erect, columnar trunks and large, compound leaves.

Question 18

List and explain the characteristics of ferns. (4)

Answer 18

As a group, ferns are either terrestrial or epiphytic (growing upon another plant). They:
* have roots, stems and leaves.
⁃ The roots grow out of the horizontal stem (rhizome) that grows partially underground.
- The leaves, fronds, are deeply divided and
are characteristically coiled in the bud.
* have vascular tissue (xylem and phloem). The xylem tracheids are strengthened by lignin. There are no vessels.
* have a thin cuticle and stomata. reproduce by means of spores. The spores are released from dehiscent sporangia, which grow on the back of the sporophylls.
dehiscent = to burst open, releasing spores
sporophylls = spore-bearing leaves
produce motile male gametes (sperm) which, like mosses rely on water for fertilization. For this reason they are usually found in moist environments.
* have an independent sporophyte. This is in contrast to the sporophyte of mosses which is entirely dependent on the gametophyte.
How can one recognise ferns?
Most ferns can be confused with other plants like cycads and many palms which also have large leaves (fronds) with a central stalk or rachis flanked by rows of narrow leaflets on both sides.

Answer 19

There are no flowers, seeds or cones.
The new leaves are coiled up and unrolled from base to tip as they develop.
This is to protect the dividing cells which are right at the tip of the leaf. Higher plants have the diving cells set back from the tip and are therefore not vulnerable to damage. - adaptation
Sporangia are found on the undersurface of the leaves. They often occur in clusters called sori. singular: sorus
With sori on under-surface of sporophylls

Question 20

What 2 characteristics of ferns are easy to see?

Answer 20

Sori on the under-surface of sporophylls and new leaves that are coiled up and unroll from base to tip as they develop.

Question 21

Why can ferns grow in drier places than mosses?

Answer 21

Ferns have proper roots with water-conducting tissue, xylem, for the absorption and transport of water from the soil.
Ferns have a waxy cuticle which helps prevent the loss of water from the leaves.

Question 22

What make up seed-bearing plants?

Answer 22

Seed-bearing plants include the two major recent plant groups, the:
* Cone-bearing plants (Gymnosperms)
* Flowering plants (Angiosperms)

Question 23

Seed-bearing plants share with ferns:

Answer 23

1. a plant body differentiated into root, stem and leaf.
2. presence of vascular tissue.
3. a dominant and
   independent sporophyte
   generation.

Question 24

Seed plants differ from mosses and ferns in that:

Answer 24

he gametophyte in seed plants has been reduced in size, usually only a few to a dozen cells. The female gametophyte is not independent but is embedded in the sporophyte and is thus less vulnerable to environmental stress than the gametophytes of bryophytes and ferns. In the bryophytes and ferns the gametophyte is independent.

Question 25

Fertilisation and spores of seed-bearing plants.

Answer 25

gametes do not depend on water for fertilisation. Spores of seed plants are either
male (microspores) and female megaspores), ie they are heterosporous. A reminder - mosses and ferns are homosporous, i.e. all spore are alike.

Question 26

Define megaspore.

Answer 26

megaspore = produced by meiosis, forms the female
gametophyte and is part of the ovule of seed plants

Question 27

Define microspore.

Answer 27

microspore = produced by meiosis, forms the
male gametophyte or pollen grain of seed plants

Question 28

Major evolutionary advancements of seed plants and what they meant.

Answer 28

1. The plant body is generally more complex, e.g. stems branch laterally and there often is secondary growth (increase in the width of stems produced by vascular cambium).
   This allows these plants to grow taller enabling them to receive more sunlight.
2. Pollen grains are produced from microspores.
   The microspore produces the male gametes (sperm cells).
   Pollen grains are transported by various means (wind, water, animals) to the female structures, where fertilization occurs.

Question 29

How does the pollen tube work?

Answer 29

The pollen grain develops a pollen tube in which the non-motile male gametes are carried directly to the female gamete in the hole. The pollen tube has thus eliminated the need for water to transport male gametes for
fertilisation.

Question 30

What is an adaptation of seed-bearing plants to do with seeds?

Answer 30

1. Resistant seeds are produced. A seed includes the embryonic plant (sporophyte), food-storage tissue and hardened protective covering (seed coat).

Question 31

Explain what the seeds of a seed-bearing plant do/ their importance.

Answer 31

The seed:
allows a plant embryo to lie dormant until conditions become suitable for its germination.
⁃ has food for the embryo’s needs in early growth and development.
The seed represents an important improvement over the spores of ferns and mosses which have a limited capacity for survival.

Question 32

When were cone bearing plants dominant?

Answer 32

dominant land plants in the age of dinosaurs

Question 33

Characteristics of cone-bearing plants

Answer 33

1. Gymnosperms are mostly trees with leaves that are usually simple and needle-like with a single vein or, less commonly, strap-shaped with multiple veins.
2. Gymnosperms are characterised most of all by their reproductive structures which are carried on open spore-bearing leaves (sporophylls) arranged into well-defined male and female cones.

Question 34

Reproductive structures of gymnosperms

Answer 34

The reproductive
structures (sporangia) are
termed the ovule (megasporangium) in the female cone and pollen sac (microsporangium) in the male cone.

Question 35

Why are gymnosperms heterosporous?

Answer 35

Gymnosperms are heterosporous because:
⁃ the male cones produce microspores that develop into pollen grains which contain the male gamete.
⁃ the female cones produce megaspores that develop into an ovule containing a female gamete.

Question 36

Fertilisation of cone-bearing plants.

Answer 36

After fertilisation the ovule develops into a seed which is exposed on an ovuliferous scale of the female cone. The seed is termed
‘naked’ as it is not enclosed by a protective ovary wall like a pod or a fruit as in flowering plants.

Question 37

Why do cone-bearing plants not have flowers?

Answer 37

Gymnosperms do not produce flowers which have an ovary. An ovary wall is actually a sporophyll with fused margins. Flowers show an evolutionary advancement after the development of seeds.

Question 38

Vascular tissue of gymnosperms.

Answer 38

The xylem tissue of gymnosperms is more
⁃ primitive than that in flowering plants as it only contains tracheids with no vessel elements.

Question 39

4 Examples of cone-bearing plants

Answer 39

1. Conifers such as yellowwoods, cedars, pines and fir trees
2. Welwitschia
3. Cycads
4. Ginkgo

Question 40

Seeds of gymnosperms

Answer 40

The seeds of very many gymnosperms are borne in cones and are not visible. These cones, however, are not the same as fruits.

Question 41

Explain conifers

Answer 41

Coniferous trees indigenous to
South African
include the yellowwoods (four species) and cedars or cypresses (three species).
Yellowwoods belong to the Podocarpaceae family.
This is an ancient, early family that was endemic to the cool, moist climate of the southern part of the ancient supercontinent of Gondwanaland.
Podocarpus refers to the seeds or “fruits’ of these trees being borne on fleshy stalks or ‘foot’.
podos = foot; carpus = fruit

Question 42

Common to most conifers

Answer 42

Podocarpus trees are evergreen and have long and narrow leaves.
There are male and female trees. The male cones are catkins (an adaptation for wind pollination) while the female tree develops round thickened, fleshy stalks each with a seed on the tip. The stalks attract fruit eaters which act as dispersing agents for the seeds.
Like all gymnosperms the developing seed is not in an ovary but lies exposed.
Podocarpus latifolius, the scientific name for what is commonly called the real yellowwood, is South Africa’s national tree

Question 43

When did angiosperms evolve?

Answer 43

The flowering plants or angiosperms evolved later than the gymnosperms, about 120 million years ago during the Cretaceous period. This was the period when the dinosaurs were vanishing.

Question 44

Describe angiosperms and there level of evolution.

Answer 44

Angiosperms are considered the most advanced types in the plant kingdom. They are vascular, seed-bearing plants that have two new interrelated structures that distinguish them from all other plants:
* flower, and
* fruit.

Question 45

What is the significance of the fruit and flower adaptation?

Answer 45

Both are used in a variety of ways by animals to carry out the plants reproductive processes. These reproductive strategies have been very successful as angiosperms are the largest and most diverse plant group. The 235 000 angiosperm species (this figure differs in various sources) represent approximately 80 percent of all the green plants now living. They grow in almost every habitat, except in the open ocean.

Question 46

What is a flower?

Answer 46

the flower is the organ of sexual reproduction.

Question 47

What is the structure of a flower?

Answer 47

A typical flower consists of a series of modifed leaves arranged in four whorls- the calyx (often green), corolla (often coloured), stamens (male whorl) and carpels (female whorl). The calyx and corolla together are termed the perianth. The modified leaves making the stamens and carpels are analogous (equivalent) to the sporophylls that make up the cones in cone-bearing plants.

Question 48

What purpose do flowers serve?

Answer 48

Flowers often attract pollinators
who transport pollen to a stigma (receptive surface) of a carpel.

Question 49

define pollinators

Answer 49

pollinators = animals that move pollen from the male anthers of a flower to the female stigma of a flower to accomplish fertilization

Question 50

define a carpal

Answer 50

carpel = a female reproductive organ in a
flower, enclosing the ovules. It consists of the stigma, a style and ovary

Question 51

The advantage of pollinators is that:
(2)

Answer 51

1. plants remain genetically strong as self pollination is avoided. Pollinators will take the pollen to distant unrelated plants of the same species.
2. pollination by pollinators is not wasteful; it sother precise as the animals carry the pollen to another flower of the same species which could be some distance away. While pollination by wind is often very wasteful and imprecise.

Question 52

Why are flowering plants so diverse?

Answer 52

The increased diversity of flowering plants is
closely related to the increased diversity of insects, which carry pollen from flower to flower and thus ensure reproduction.

Question 53

Structure of a flower in respect to female/male

Answer 53

flowers contain the male (stamen) and/or female (carpel) reproductive organs.

Question 54

Where are the male gametes found?

Answer 54

⁃ The male gametes are found inside the pollen grains which are produced by the anthers of the stamen.

Question 55

Where are the female gametes found?

Answer 55

⁃ The female gametes are inside the ovules which are enclosed by the ovary (the future seedcase) of the carpel. (ovary wall)

Question 56

What is the value of pollination? 1.

Answer 56

Without pollination there would be no fertilization; which is vital for the production of fruit crops (e.g. apples, pears) and seed crops (e.g. maize, wheat) - supplying man with food.
Natural ecosystems would collapse without pollination.
preserve life + ecosystems
Food+ shelter

Question 57

What is the value of pollination? 2.

Answer 57

Pollination also plays an important part in plant breeding experiments aimed at increasing crop production through the creation of genetically superior types.

Question 58

What is a fruit? (4)

Answer 58

1. Fertilisation of the female gamete takes place within the ovule. Ovules are enclosed in an ovary and are not naked and unprotected on a cone scale (sporophyll) as in the gymnosperms.
2. After fertilisation the ovary matures and contains the seeds (mature ovules). The seeds are thus protected by the ovary wall.
3. The mature ovary and its contents is called a fruit.
4. Fruits are very valuable in ecosystems as they serve as a means of seed dispersal when eaten by animals.

Question 59

flowering plants consist of two classes:

Answer 59

1. Monacotyledons (65 000 species)
2. Dicotyledons (170 000 species)

Question 60

Explanation of monocots

Answer 60

Even though there are fewer monocotyledon species than dicotyledons, the monocotyledons are economically extremely important.

Question 61

Most economically NB monocot group?

Answer 61

The most important group is the grasses that include all the grains (rice, wheat, maize, sorghum, etc) and the pasture grasses.
Grasses have evolved to become highly specialised for wind pollination; they produce vast quantities of light, dry pollen and have large feathery stigmas to trap the pollen.

Question 62

Other economically NB groups of monocots?

Answer 62

Other economically important monocotyledon groups that produce food are the palms, bananas and the onions.

Question 63

What are many monocots grown for, explain.

Answer 63

Many monocotyledons are grown for their flowers,
e.g. gladiolus, freesias, strelitzia,
amaryllis, red hot poker and orchids. The largest family in this group and in the flowering plants as a whole) by number of species are the orchids, with about 20 000 species.

Question 64

Distinguishing features of monocotyledons (8)

1. Seed
2. Leaves
3. Flowers
4. Perianth
5. Vascular
6. 2ndary thickening
7. Roots
8. Pollinators

Answer 64

• The embryo has a single seed leaf (cotyledon).
• The leaves are usually narrow with parallel veins; exceptions include the arum lily, banana and strelitzia.
• The flower parts usually occur in multiples of three.
• The perianth segments are similar, i.e. they are not differentiated into sepals and petals.
• The vascular bundles are scattered in the stem.
• No secondary thickening occurs as there is no cambium. Monocotyledons therefore do not generally reach great size. The Wild date palm (Phoenix reclinata) and Natal wild banana tree (Strelitzia nicolai) are exceptions.
• The roots are fibrous and adventitious and grow from the base of the stem.
• Pollination is often by wind

Question 65

Briefly explain dicots

Answer 65

Dicotyledons are the more numerous group. They include evergreen and deciduous broad-leaf trees, flowering plants and crop plants such as spinach, carrots and tomatoes.

Question 66

Distinguishing features of dicotyledons (8)

1. Seed
2. Leaves
3. Flowers
4. Perianth
5. Vascular
6. 2ndary thickening
7. Roots
8. Pollinators

Answer 66

• The embryo has two seed leaves (cotyledons).
• The leaves usually are broad with a network of veins.
• The flower parts are in multiples of four or five.
• The perianth consists of sepals and petals.
• The stem contains a ring of vascular bundles.
• Secondary thickening is common as cambium is present.
  Some dicotyledons
  therefore can reach great heights.
• The root, a tap root, develops from the radicle of the embryo. (radice → part of embrup that develops into a root)
• Most angiosperms are insect pollinated.
  The diagram below shows the four flower whorls as found in dicotyledons and gives the general function of each.

Question 67

Relate the 4 flower whorls of dicots and pollination

Answer 67

Four flower whorls as found in dicotyledons.
There are many variations of this four-whorl arrangement - in colour, size and shape. This diversity can be related to the way pollen is transferred. (wind, insect)
It could be said that flowering plants and insects co-evolved.

Question 68

Structure & function of carpel of dicot

Answer 68

Carpel (female part)
⁃ stigma - sticky surface to which pollen adheres
⁃ style- slender section joining stigma to ovary
⁃ ovary - female organ where - ovules are formed. After fertilisation matures into fruit.
⁃ ovule - contains female gamete. After fertilisation forms a seed.

Question 69

Structure & function of stamen of dicot

Answer 69

Stamen (male part)
⁃ anther - male organ where pollen grains are formed
⁃ filament - flexible stalk

Question 70

Structure & function of perianth of dicot

Answer 70

Perianth - Calyx & Corolla combined
Calyx - protects unopened bud
⁃ sepals - whorl of modified leaves
Corolla - attracts pollinators
⁃ petals - whorl of modified leaves

Question 71

What is the part of flower below main area of flowers and other structures?

Answer 71

Receptacle - supports floral parts