Botany - WildlifeCampus · Introduction to Plants What is a Plant? All life on earth belongs to one of five kingdoms. ... Plant morphology refers to the external structure of the

– Game Ranging / Field Guiding Course

This course material is the copyrighted intellectual property of WildlifeCampus. It may not be copied, distributed or reproduced in any format whatsoever without the express written permission of WildlifeCampus

1

Botany © Copyright

Botany



2

Botany © Copyright

Module # 9 – Component # 1

Introduction to Plants

What is a Plant?

All life on earth belongs to one of five kingdoms. Botany is the study of the Plant Kingdom.

A general definition of a plant: An organism that contains chlorophyll and is

autotrophic (capable of making its own food from inorganic materials by the process of

photosynthesis). This definition, however, does not incorporate

plants such as fungi, some bacteria and parasitic plants which are heterotrophic (an organism that

depends on organic matter already produced by other organisms for its nourishment).

Plants are differentiated from animals in that they possess cellulose cell walls and generally non-

motile (unmoving). Additionally, most plants tend to grow indefinitely while growth in animals

usually ceases at maturity.



3

Botany © Copyright

Plant Groupings Plants are broadly divided into those that possess true roots, stems and leaves

and those that do not.

Plants that do not possess true roots, stems and leaves are called Thallophytes.

Thallophytes are further characterised by the fact that

their reproductive cells are not protected by vegetative or sterile cells. The Thallophytes

include bacteria, algae and fungi. Thallophytes are also

occasionally known as Lower Plants.

Thallophytes are described in detail in the next component of

this Module. All remaining plants have reproductive cells that are protected by sterile cells and

true roots, stems and leaves. A small group of these plants lack vascular conducting tissue - these are the liverworts and the mosses. All other plants

have a specialised conducting tissue and are known as vascular plants.

Vascular plants are divided into non-seed-bearing plants such as ferns and the more advanced seed-bearing plants. The seed-bearing plants are divided into gymnosperms (naked seeds) and angiosperms (seeds protected within an

ovary). Angiosperms are further divided into monocotyledons and dicotyledons.

The simplest plants are the bacteria and blue-green algae. These organisms have been put into their own kingdom – Kingdom Monera. These comprise a

group known as Procaryota, whose members have no distinct nucleus in their cells. All other plants are classed as Eucaryota.

Bacteria is examined more closely in the next component: - Lower Plants



4

Botany © Copyright

Plant Morphology Plant morphology refers to the external structure of the plant.

(Image source: biology.tutorvista.com)



5

Botany © Copyright

Stems Stems are elongated organs that form the axis onto which leaves and buds are

attached. The place on the stem where leaves and buds are attached is called a node. The space between two nodes is called the internode. All stems, whether

short or long, horizontal or vertical, are characterised by the presence of nodes and internodes.

Stems provide support for leaves and other appendages. They facilitate photosynthesis by raising leaves towards the sun. Stems conduct water, minerals,

food and hormones from roots to leaves and from one part of the stem to another. Stems produce new living tissue and store food and water.

Stems may be modified to form:

Rhizomes a horizontal, underground stem Canna

Corms a vertical, short, thickened underground stem Gladiolus

Bulbs like corms but possessing leafy scales in which food is stored

Onion

Tuber enlarged ends of slender rhizomes Potato

Stem spikes modified stems or outgrowths of stems. Pyracantha

Stolons above-ground horizontal stems Strawberry

Stem tendrils slender modified stems that attach the plant to a support

Grape

Stems provide us with, amongst other things, wood, paper, gum, tannin, latex

(crude natural rubber is obtained from the latex of rubber-yielding species) and resins.



6

Botany © Copyright

Roots

The root is that part of a plant which tends to grow downwards away from

light and towards water. It bears neither leaves nor buds and usually ends in a special protective structure called the root cap. Behind the root cap, the outside

layer of the root bears fine hairs called root hairs, which are the chief organs of absorption. The roots of a plant are collectively termed the root system.

A tap root system consists of one main root from which lateral roots radiate. Some desert plants

have a rapidly growing tap root system which enables them to

reach deep sources of water.

A fibrous root system consists

of several main roots that branch to form a dense mass of

intermeshed lateral roots.

Roots that develop from organs

other than roots are called adventitious roots. There are many examples of adventitious

roots.

Prop roots develop at the nodes of stems and function as roots. They also assist in providing

support to the plant.

Aerial prop roots are produced by many tropical trees like mangroves.

In some instances, roots develop in clusters on stem internodes. These root clusters form a flat adhesive pad against a structure.

The two principal functions of roots are those of absorption and anchorage.

Roots also perform the function of conduction and some roots act as food storage organs.



7

Botany © Copyright

Leaves

A typical dicotyledonous foliage leaf is composed of a blade and a petiole. The

shape of the apex, the margin and the base compose the overall shape of the leaf blade. The apex of a leaf may be pointed or rounded. The margin may be entire,

having no indentations whatsoever, or it may be toothed, scalloped, wavy or cut into lobes. The base of the leaf may take on many forms including rounded, heart-shaped and tapering.

The petiole is that portion of the leaf that attaches the blade to the stem. If the petiole is attached to the blade at the middle on the underside, the leaf is called a

peltate leaf. If the petiole is absent and the blade is mounted directly onto the stem, the leaf is said to be sessile.

Monocotyledonous leaves such as grasses do not have distinct petioles. Instead, the leaf is composed of a blade and a sheath. The sheath surrounds the

stem. A small flap of tissue extends upward from the sheath and is called the ligule.



8

Botany © Copyright

There are two kinds of leaf blades: simple and compound. In a simple leaf the blade is all one unit whereas the blade of a compound leaf is composed of several separate leaflets. The difference between a leaf and a leaflet is that buds occur in

the axils of leaves but not in the axils of leaflets.

When leaflets develop from the rachis (a continuation of the petiole) the leaf is termed pinnately compound. When the leaflets develop from one point at the tip of the petiole the leaf is said to be palmately compound.

The arrangement of veins of a leaf is termed venation. There are two principal

types of venation: parallel venation and net venation. In parallel venation, there are usually one or more large veins which run parallel to each other. In net

venation, there are one or more prominent veins from which smaller veins branch off to join with other small veins. The type of venation exhibited by leaves is the best indicator of whether it is a mono or dicotyledonous plant. Monocotyledons

have parallel venation, while dicot plants have net venation.



9

Botany © Copyright

Thorns

Thorns are quite simply modified leaves. They have a similar internal structure

and for some plants are still the site for photosynthesis. Thorns are an evolutionary adaptation of the plant as a means of protection from herbivores.

Plants have only been halfway successful in this endeavour. Since thorns are an evolutionary ‘response’ due to animals, it is only reasonable that animals themselves should have shown a similar evolutionary ‘reaction’ to the plant’s

new protectionism. Examining animal / plant interactions and associations today reveal may examples of convergent or parallel evolution. Many browsers eat

exclusively from thorn trees. The animals have adapted to these ‘thorny’ problems, and the plant has adapted to being occasionally eaten.

Thorns show a wide variation in form, and mostly grow together with leaves on trees. There are however, a large group of plants where thorns not only function

in protection from animals, but also from the climate. Desert dwelling cacti and other succulents only have thorns. Thorns reduce the amount of water being lost

from these plants (transpiration) and regulate when their stomata (tiny holes for gas exchange) open and close.



10

Botany © Copyright

Plant Physiology

Photosynthesis and Respiration There are two chemical processes that occur in all true plants. These are photosynthesis and respiration. Photosynthesis and Respiration are very

complex processes. A brief description of both processes will suffice.

During the process of photosynthesis light energy from the sun is converted into chemical energy.

It is this chemical reaction that distinguishes plants most strongly from

animals.

Atmospheric carbon dioxide absorbed through the leaves, and water which is taken up from the soil by the roots are used in the process. Carbohydrate

molecules containing large amounts of energy are produced. Oxygen which is the main source of atmospheric oxygen is given off. The photosynthetic

reaction can be summarised by the following equation:

6CO2 + 6H2O + C6H12O6 + 6O2

Chloroplasts are the site of photosynthesis. Light energy is absorbed by the chief pigment (which accounts for the green colour of plants), chlorophyll,

present in the chloroplasts and which drives the photosynthetic process.

The rate of photosynthesis is influenced by internal factors - the structure of the leaf and its chlorophyll content. There is a decrease in the photosynthetic rate when the carbohydrate is manufactured more rapidly than is transferred from the

cell. Finally, photosynthesis slows down when there is a water deficit in the cells.

Light Energy



11

Botany © Copyright

External factors which influence the rate of photosynthesis are: temperature; light intensity; quality and duration of light; the availability of carbon dioxide; water supply; and the mineral content of the soil.

Respiration is defined as the oxidation of organic substances within the cells

and the release of energy. A cell must be able to use the energy stored in food produced through the process of photosynthesis.

Thus, a living cell breaks down the food and traps the energy in the form of the energy-transport molecules called ATP and NADP. Food and oxygen are used and

carbon dioxide, water and energy are the end products.

Respiration can be summed up by this simple equation which is the exact opposite of the photosynthesis equation:

C6 H12O2 + 6O2 6CO2 + 6H2O + energy To compare photosynthesis and respiration, here is a simplified table:

Photosynthesis Respiration

Carbon dioxide and water are used Oxygen and food are used

Food (Carbohydrate) and oxygen are

produced

Carbon dioxide and water are

produced

Energy from light is trapped Energy from food may be

temporarily stored in ATP or lost as heat.

Only chlorophyll-containing cells carry out photosynthesis

Every living cell carries out respiration

Occurs only in light Occurs in light or darkness

Occurs in chloroplasts Occurs in cytoplasm and in mitochondria

Photosynthesis must exceed respiration for growth to occur

Factors affecting the rate of respiration are the amount of water available, temperature, availability of stored food and the amount of gaseous oxygen.

oxidation



12

Botany © Copyright

Soil and Minerals Soil is the natural medium in which plants grow. Plants absorb water and

minerals necessary for their development from the soil.

Soils contain both mineral and organic matter. The organic matter of the soil is derived from plants and animals. Partially decomposed organic matter in soils is called humus. The mineral content comes from the continual weathering of

rock. The kind of rock and the degree of weathering determines the mineral content of the soil.

Mineral elements are divided into macronutrient elements and micronutrient elements. The macronutrients, so called because they are needed in large

quantities, are: nitrogen, sulphur, phosphorus, potassium, magnesium and calcium. Micronutrients include iron, boron, manganese, copper, zinc, chlorine and

molybdenum.



13

Botany © Copyright

Plant Responses All plant cells respond to environmental changes.

Phototropism is the growth of the plant in response to a light

source.

Geotropism is the plant’s growth in response to gravity. Roots

demonstrate positive geotropism by growing downwards, whereas

shoots show negative geotropism by growing away from the force.

Chemotropism is the response to

a chemical stimulus. Motile algae and bacteria move in response to chemicals.



14

Botany © Copyright

Photoperiodism is

the response of plants to changing day and night length. Such

responses include plant and seed

dormancy and leaf abscission (shedding

of leaves).

Thigmotropism

describes a plant’s response to contact. Tendrils and twining

stems of climbing plants are prompted

to curl around supports which touch

them. The leaves of very sensitive plants normally collapse if

touched. This response may also be

known as Thigmonasty.



15

Botany © Copyright

Tannin

One further plant response that bares

mentioning is based on recent scientific work in this interesting field. This

response concerns a plant chemical know as tannin. This is a toxic chemical that also makes plant leaves unpalatable.

It has been found that in certain species

of Acacia that when an animal begins feeding on the tree, the tree responds by producing tannins in their leaves.

This makes them taste bad and causes the animal to move to a different part of

the tree or to a new tree completely. Therefore, animals don’t spend all their time on one tree, but move frequently

between trees. This defensive response aids in the tree not being

severely defoliated in a short space of time. This has been known for some time.

However, in a study conducted in the early 1990’s it was found that in addition to the

trees producing tannins when they are eaten, they also produce and release a

secondary chemical into the air that is taken up by surrounding trees. These trees in turn begin tannin production before any feeding on them takes place.

This topic and related issues are fully described in our Wildlife Management

Course. Plants can also be classified according to their water needs.

Xerophytes are those plants able to live in very dry places

Hydrophytes are plants which live in water or very wet soil

Mesophytes thrive on a moderate water supply

Halophytes have evolved to live in very salty soils.



16

Botany © Copyright

Plant Reproduction Many plants have both sexual and asexual means of reproduction.

Some, such as bacteria and blue-green algae, demonstrate asexual reproduction

only. It may be simple as is the case of bacteria. A bacterial cell simply divides to produce two - a procedure known as fission.

When fragments of filamentous algae separate and become individuals, they are said to arise by fragmentation. Another form of asexual reproduction is

sporulation, the formation of spores. The protoplasm undergoes division and the separate small masses of protoplasm become spores. In this case the spores give rise to new plants.

As you will have ascertained, as plants evolved they developed more complex

mechanisms of reproduction as their own forms became more varied and complex. Some biologists have described plants as living fossils since many species have changed little if it all over billions of years. Today they now grow side

by side with other members of their Kingdom that only evolved millions of years later. Unlike the Animal Kingdom, this gives natural scientists the opportunity to

compare these species side by side. As a method of reproducing, sexual reproduction is a much younger method.

Through three examples we will be able to show the progression of reproduction as plants evolved.

Sexual reproduction involves the formation of sperm cells and eggs which fuse.

This occurs in a variety of ways. Firstly, we will study a non – seed bearing plant.



17

Botany © Copyright

Ferns

Ferns probably evolved around 430 million years ago, and within 70 million years

became the dominant plant form. They evolved a variety of sexual reproduction, but in a primitive form.

In this specific scenario spores are produced in special structures called sporangia which usually develop on the underside of the leaf. At maturity,

each sporangium releases its spores. This is called sporulation

Each spore develops into a heart-shaped gametophyte anchored to the soil

by rhizoids. Multicellular sex organs develop on the under surface of the gametophyte.

The sex organ in which sperm cells develop is called the antheridium and the organ in which the egg develops is called the archegonium. The sperm swims

to reach the egg and fuses with it. The now fertilised egg gives rise to a new fern plant. The gametophyte shrivels and disappears.

Seed - bearing plants you will recall are divided into gymnosperms and angiosperms.



18

Botany © Copyright

Pines

Pine trees are the quintessential gymnosperms. They are also commonly

known as conifers – a reference to their reproductive structures. Many of the large Northern Hemisphere trees are conifers and include among 546 other

species, Redwoods, cedars, Giant sequoias and fir trees. This group of trees is also mainly responsible for our lumber and paper.

Conifers have their reproductive parts located in cones that are a typical morphological feature of these trees. Generally, each tree will have “male” cones

and” female” cones. Through a process of maturing, the male cones produce male gametophytes which are released from the male cone and enter the female cone. Here the female gametophytes have matured and through a highly complex

series of mechanisms, mature seeds are produced. The seeds are released from the cone, disperse on the wind, settle in suitable habitats and germinate into new

saplings.



19

Botany © Copyright

Angiosperm Reproduction Angiosperms are the most recent evolved of plants and therefore the most

complex and consequently have the most complicated modes of reproduction.

Firstly, we must remember that angiosperms are divided up into the monocotyledons and dicotyledons. The Monocotyledons or ‘monocots’ include among other groups, all the grasses (maize, rice, wheat, barley, sugar cane,

bamboo, lawn grass and +- 10 000 other species).

The grasses are examined in the next component of this module, so please see it for more information on their reproduction.

The ‘dicots’ are probably the most special of all plant groups to most non-scientists, as they contain almost all the flowers. The need for this very large group (± 235

000 species) to have evolved flowers will become clear soon. The reproductive parts of angiosperms are to be found inside flowers – although

this is only part of the reason for their existence. The male parts are called stamens and consist of a pollen encrusted anther and stalk-like filament.

Usually several stamens surround one central carpel (female parts) consisting of an ovary, style (stalk) and stigma (opening). Genetic material is carried in pollen for the male portion and in the ovaries for the female.

Unlike in monocotyledons, pollen in dicots does not rely on the wind for

pollination but rather needs a pollinator, usually in animal form. The most common are obviously insects, but birds and even certain mammals are relied

upon to carry pollen for these plants. This is the main reason for the wide diversity of flowers. They are needed to attract the correct pollinator or pollen vector.

Some flowers are designed in such a way as to attract a variety of vectors,

while others are specialised and will only allow specific vectors to take pollen from them.

The specialised bills of Sunbirds and Hummingbirds, for example are adapted for certain flowers only. The bird can only get nectar from these flowers and thus the flower will only allow pollen to attach to that specific bird.

The Baobab tree can only be pollinated by one species of bat. In this scenario, each species relies directly on the other for its survival. If all the bats die, the

tree cannot propagate itself. This is also an example of co-evolution between two completely different species.

Another example is the Coco d’ Mur, which has evolved a rotten flesh odour specifically to attract certain species of fly.



20

Botany © Copyright

These examples have highlighted the main function of flowers – to attract the correct vector. This is the reason for their bright and varied colouration and forms. This has led scientists to conclude that insects and birds can indeed see

colour. Nectar incidentally, the most common attractant of vector to flowers, is simply a form of sugared water.

The transfer of the pollen from one flower to another is a relatively simple

procedure. The vector usually just makes contact with the flower and in doing so gets pollen stuck to its body. Pollen is not actually sticky in the sense of glue, but rather is very spiky at the microscopic level. The pollen literally hooks in the

vector, whether on its fur, feathers, leg hair or clothing. The vector then visits a second flower of the same species, and though contact with the second flower

deposits pollen from the first. The pollen lands onto the stigma, travels down a pollen tube and into the ovary.

The pollen fertilises an egg, which develops into a seed. The ovary once filled with fertilised eggs develops into another form, a fruit or vegetable which are

common examples. The seed will be dispersed when the fruit or other structure becomes detached from the plant.

Co-incidentally, angiosperms began to evolve ± 120 million years ago, and were the dominant plant form (as they continue to be today), from 65 million years

ago – the beginning of the rise of the mammals.

Documents

Botany - WildlifeCampus · Introduction to Plants What is a Plant? All life on earth belongs to one of five kingdoms. ... Plant morphology refers to the external structure of the