SCI6: CLASSIFICATION OF PLANTS

This unit covers part of Primary Six Science, Term one

LESSON   1:     FLOWERING PLANTS.

  • Plants are living components of the environment
  • A plant is a green growing living thing on the earth’s surface
  • Plants are the primary sources of food to both animals and people

Classification of plants

Classification of plants means grouping plants according to their different characteristics.

Plants are classified into two;

  • Flowering plants
  • Non-flowering plants.

FLOWERING PLANTS

Flowering plants are plants that bear flowers and reproduce by means of seeds.

Flowering plants are made up of two systems

  • Shoot system
  • Root system

Shoot system is the part that develops from the plumule.  It grows above the ground.

Flowering plants are sub-divided into two;-

  • Monocotyledonous and

Characteristics of dicotyledonous plants.

  • They have a tap root system.
  • Their seeds have two cotyledons.
  • Their seeds undergo epigeal germination
  • They have network leaf venation.

Characteristics of monocotyledonous plants.

  • The seeds of monocotyledonous plants have only one cotyledon
  • They have a fibrous root system.
  • They have a parallel leaf venation
  • Their seeds undergo hypogeal germination.

LESSON   2      :       PARTS OF A FLOWERING PLANT

  • Flowering plants have both root system and shoot system
  • The root system is the part that grows in the soil
  • The root system involves main root, lateral roots, root hair and the root cap.

Types of root systems.

There are basically two types of root systems namely;

  • Tap root system and
  • Fibrous root system
  • Tap root grows directly from the radical of the germinating embryo
  • They are commonly found in dicots.
  • Fibrous roots grow without a tap root or main root.
  • They are commonly found in monocots.

Draw structures showing parts of a tap root and fibrous root systems.

 Tap root systemFibrous system
Image result for tap root system

 

  

Function of roots to a plant

  • Roots hold the plant (shoot system) firmly in the soil
  • Root hairs absorb water and mineral salts from the soil

NB: Mineral salts enter by a process called active transport.

  • Some plants store their food in swollen roots.
  • Prop roots provide extra-support to plants
  • Breathing roots absorb oxygen especially in the mangroves.
  • Root nodules of legumes store nitrogen-fixing bacteria that improves soil fertility.

Importance of roots to people:

  • Swollen roots with stored food are sources of food to people e.g. Cassava, Sweet potatoes,& Carrots.
  • Some plant roots acts as herbs to cure some diseases e.g. Mangoes, Blackjack, Muringa plant, etc.
  • Big dry roots acts as source of wood fuel to people.
  • Some big roots can be used in making craft items.

LESSON   3 :    TYPES OF ROOTS

There are basically two types of roots names:

  • Primary roots and
  • Secondary rots
  • Primary roots are roots that grows directly from the radical of a seed. Tap roots and fibrous roots are the examples of primary roots
  • Secondary roots are roots that develop from the other parts of a plant like the stem and leaves.
  • They mainly grow to give extra support to the plant with weak stems.

Examples of secondary roots include;

  • Prop roots
  • Aerial roots
  • Breathing roots
  • Roots of rhizomes and corms.
  • Buttress roots
  • Clasping roots
  • Stilt roots
  • Prop roots are common to plants such as, maize, millet, sorghum and wheat.
  • They mainly grow to provide extra-support to the plant especially at the flowering stage.
  • Clasping roots enable plants with weak stems climb other plants and rap sunlight energy.
  • Stilt roots are found on plants which commonly grow in muddy or swampy areas. They are also known as breathing roots.
  • They take in air for respiration of roots. This is because soil with a lot of water does not have enough ai

 Note: some plants have swollen roots which store food for the plant.

They have terminal buds surrounding their leaf bases.

LESSON 4:PLANT STEMS.

  • The stem is the biggest part of the shoot system of a plant.
  • It holds leaves, flowers, fruits, branches and terminal bud

Types of stems

  • Upright stems:
  • Underground stems
  • Climbing stems.
  • Examples of upright stems include paw-paws, mangoes, maize, beans etc
  • Examples of underground stems are; stem tubers, bulbs and corms.

Climbing stems are weak stems of plants that cannot support themselves upright.

Plants climb others for support in order to get light

How plants climb others

Plants with weak stems climb other by;

  • Use of tendrils
  • Use of hooks

  • Twining or clasping

Note:

  • Stem tubers are crops with underground swollen stems which store food.
  • Plants with such include; cocoyam and Irish potatoes
  • Rhizomes commonly grow horizontally under the ground with stored food. E.g. ginger and canalilies.
  • Corms grow vertically under the ground with stored food rich in carbohydrates.

Functions of stems to a plant

  • They hold and space out leaves to receive the sunlight energy
  • Stems transport water and mineral salts from the roots to the leaves
  • Green stems help in the process of photosynthesis
  • Stems conduct manufactured food in the leaves to all other parts of the plants.
  • Stems hold flowers and fruits for easy pollination and dispersal
  • Some plant stems have thorns for protection

Functions of stems to people.

  • Some plant stems act as a source of food to both people and animals
  • Big stems provide people with timer and poles for construction
  • Plant stems act as a local medicine to cure some animal diseases
  • Some plants are harvested to provide wood fuel to people
  • Some plant stems are used for propagation ie cassava, sugarcanes and some flowers.

LESSON   5 :    PLANT PROPAGATION 

  • Propagation is artificial methods used to obtain new plants
  • Some plants are propagated by the use of stems with terminal buds

Examples of plants propagated by the use of their stems include;

  • Cassava
  • Sugarcanes
  • Sweet potatoes
  • Some plants are propagated using bulbs such as onions, garlic and spider lily.
  • Onions are involved in our diets to provide iron to our bodies.
  • Some plants are propagated using suckers such as banana plants, pineapples and sisal plants.

Draw a structure showing a sucker of a banana plant.

  • Some plants are propagated using tubers such as; Irish potatoes, cocoyam.

A structure showing parts of stem tuber.

  • Some plants are propagated with the help of corms (kind of underground stems) e.g coco yams, gladiolus and crocus. 
  • Example include, ginger canalily, zoysia grass and turmeric.Some plants are propagated using the rhizomes.
  • Rhizomes are swollen underground stems with stored food and grow horizontally.

LESSON 6 :     PLANT LEAVES

  • Leaves are the green parts of a plant with stomata for gaseous exchange.
  • Leaves have chlorophyll to trap sunlight energy and manufacture its starch.
  • Leaves also form the shoot system of a plant.
  • A leaf is fixed between two internodes on a plant stem or branch.

PRACTICAL ACTIVITY ABOUT DIFFERENT TYPES OF LEAVES (COLLECTING AND OBSERVING DIFFERENT LEAVES FROM THE ENVIRONMENT)

Functions of the above parts.

  • It has a surface area for easy trapping of sunlight energy by the help of chlorophyll
  • It’s where the stomata are found.
  • It helps in the manufacturing of starch

Stomata

  • It’s called stoma for singular and stomata for plural.
  • They are small holes on the leaf where gaseous exchange takes place.
  • They also open to allow water escape during the process of transpiration.
  • The stomata also let in carbondioxide by diffusion during day time and oxygen during night time.

Leaf veins.

  • They are hollow to allow distribution of water and nutrients within the leaf

Leaf apex.

  • It’s the sharp tip part of a leaf to provide protection to the leaf

Leaf stalk / petiole

  • This provides attachment of the leaf to stem or a branch.

Note: there are mainly two processes that take place in plant leaves namely;

  • Photosynthesis and
  • Breathing

LESSON   1      :       TYPES OF LEAVES

Types of plant leaves

  • There are two types of plant leaves which include;
  • Simple plant leaves
  • Compound leaves

Simple leaves

Simple leaves are leaves completely not divided.

Examples of simple leaves include;

  • Simple serrated leaf
  • Simple palmate leaf
  • Simple divided entire leaf
  • Simple lobed leaf
  • Simple entire leaf.

Dawn structure showing different examples of simple leaves

  • Compound leaves are characterized with a divided lamina
  • Compound leaves have more than one leaf-let on one leaf blade or stalk.
  • A compound leaf has completely separate portions called leaflets
  • Each leaflet has a small stalk which is attached to a common leaf stalk.

Examples of compound leaves;

  • Compound trifoliate eg. Beans leaves
  • Compound bipinnate eg. Jacaranda leaves/ mimosa plant
  • Compound digitate leaf eg. Silk cotton leaves
  • Compound pinnate e.g. acacia leaves /encalyptus

Drawn structures showing examples of compound leaves

 

LESSON   2      :       USES OF LEAVES AND LEAF VENATION

 

Leaf venation

  • Plant leaf venation refers to the arrangement of veins in a leaf.
  • Veins in a plant leaf help in the circulation or distribution of water and mineral salts.

Types of leaf venations:

  • There are basically two types of plant leaf venation namely;
  • Network leaf venation
  • Parallel leaf venation
  • Plants with a network leaf venation have a structure in the lamina like a net in their leaves
  • Network leaf venation is a characteristic of dicotyledonous plants.

 

Note:

  • Network leaf venation is common in both simple and compound leaves.
  • Parallel leaf venation is where leaves have veins running parallel from the leaf stalk to the tip or apex.
  • Parallel leaf venation is a characteristic of monocotyledonous plants.

Drawn structure showing a leaf with parallel leaf venation.

Note:

  • Parallel leaf venation is mainly found in simple entire leaves.

Learner’s activity

  1. Write one sentence to show the meaning of the following;
  2. Venation
  3. Parallel venation
  4. Draw the structure of a simple lobed leaf
  5. Give two examples of compound leaves
  6. Which of the leaves A and B is a compound leaf?

 

LESSON 3       :       PHOTOSYNTHESIS IN PLANTS

Photosynthesis in plants

  • Photosynthesis is the process by which plants manufacture their own food.
  • The word “photo” means light, “synthesis” means to make or “buildup”

Raw materials needed

There are two raw materials needed during the process of photosynthesis.

Water

  • To dissolve the mineral salts in a leaf.
  • Also to make the leaf soft for easy diffusion of starch.

Carbon dioxide gas

  • This is synthesized to make carbon
  • Both water and carbon dioxide combine to build up glucose stored in the plant leaves as starch.

Conditions necessary for photosynthesis

  • Chlorophyll – to trap the sunlight energy
  • Sun light energy – helps in the breaking down of the water into hydrogen to speed up the formation of the starch.

Note:

  • Oxygen is a by-product of photosynthesis while starch is the main product.
  • Animals get oxygen from the process of photosynthesis.
  • Photosynthesis cannot take place at night due to the absence of the sunlight energy.
  • Photosynthesis is a chemical change in plants.

LESSON 4       :       TRANSPIRATION IN PLANTS

  • Transportation is also a process in plants that take place in the leaves and some stems.
  • Transpiration is the process by which plants lose water as vapour into the atmosphere
  • Transpiration takes place in plants through the stomata of leaves, lenticels and in the cuticle of stems

Note: Let the learners participate in carrying out an experiment under the guidance of the teacher

Illustration showing transpiration in plant leaves.

Image result for transpiration in plant leaves

Tree branch with plastic bag tied around it, showing transpired water inside the bag.

How plants benefit from the process of transpiration (importance);

  • Plants are able to absorb water and mineral salts from the soil through their roots up to the rest of the plant parts.
  • Transpiration helps in cooling the plant during a hot day.

Note:

The transpired vapour from the plants helps in the formation of rain.

Dangers of transpiration

  • Plants lose even the useful water they need during a dry season. This may make plants dry up to death
  • It lowers the crop yields due to less water left in the plant.

Ways plants reduce the rate of transpiration.

  • Some plant leaves are modified into thorns
  • Some plant leaves have few stomata and distributed at the lower part of the leaf.
  • Some plants have leaves with a small surface area to reduce the rate of water loss
  • Some plants reduce the rate of transpiration by shedding their leaves especially during dry season e.g. deciduous plants (Mvule,Oak & fig trees)
  • Leaves have a wax-like layer to cover their stomata to limit the water loss.
  • Stems have tough cuticles and lenticels to guard against water loss.

Factors that affect the rate of transpiration in plants;

The following are the conditions that either increase or decrease the rate of transpiration;

Wind

Wind blows off the water molecules on the plant leaf giving chance or space for more vapour to come out. This increases the rate of transpiration.

Humidity:

  • Humidity is the amount of water vapour in the atmosphere.
  • High rate of humidity lowers the rate of transpiration and vice versa.

Temperature:

High temperature during hot days causes plant leaves to lose a lot of water than on cool days.

Sunlight:

Heat from the sun causes the opening of the stomata, lenticels and cuticle hence creating more chances of losing water.

Surface area of the leaf:

Plants with small surface area of their leaves lose water at a lower rate than those with larger leaf surface area.

Number of stomata:

Plant leaves with fewer stomata have a low rate of transpiration

The higher the number of stomata, the higher the rate of transpiration

Some leaves have stomata at the lower side of the leaf

NB: Most transpiration takes place in leaves

“A PRACTICAL LESSON ABOUT TRANSPIRATION IN PLANT SHOOT’’ (Through excursion)

LESSON   5      :       FLOWERS

  • The flower is the reproductive part of a plant. Therefore, it’s where the process of reproduction takes place.
  • The flower has both the female and male gametes
  • A gamete is a reproductive cell

A flower has got two parts namely;

The female part called pistil (gynoecium) and male part called stamen (androecium)

Pistil is made up of stigma, style, ovary and ovules

Stamen is made up of the filament and anther head.

The male reproductive cells are the pollen grains and female are the ovules.

Drawn structure showing parts of a flower.

Functions of the parts

Petals, the brightly coloured petals help to attract pollinating agents such as insects.

A group of petals is called corolla

Sepals– Green sepals help to manufacture food for the plant.

– Protect the inner parts of the flower at an early stage (bud    stage)

A group of sepals is called calyx

Style: is a passage of the pollen grains to the ovary

The style also supports / holds the stigma in position

Ovary. It produces the female gametes called ovules

A mature fertilized ovary turns into a fruit

Filament. Holds the anther heads in position

Anther heads. Produce male gametes called pollen grains.

Stigma. It’s strictly to receive pollen grains without falling off.

LESSON   6      :       POLLINATION

  • Pollination is the transfer of pollen grains from the anther heads to the stigma of a flower on a plant.
  • Pollination helps to allow fertilization in plants
  • Fertilization is the union of both female and male gametes to form a zygote.
  • The pollen grains are the male gametes while the ovules are the female gametes in plants.

Types of pollination.

There are two types of pollination namely;

  • Self pollination
  • Cross pollination


Self pollination is the transfer of pollen grains from the anther heads to the stigma of the same flower

Flowers with self pollination have shorter stigma compared to their anther heads.

They also have brightly coloured petals to attract pollinators

Note:

Some flowers are adapted to self pollination by:

Both the anther and stigma maturing at the same time.

Their flowers remain closed until self pollination takes place

Structure illustrating self pollination.

Image result for self pollination

cross-pollination is the transfer of pollen grains from the anther heads of one flower to the stigma of another flower but of the same type or species.

In cross–pollination, the anther heads are shorter than the stigma.

Flowers are able to carry out cross-pollination by;

  • Maturing of anther heads and stigma at different times.
  • Having one productive gamete on each plant i.e. paw-paw plants

Illustration showing cross-pollination.

Note: Agents of pollination refers to the factors that are responsible or cause pollination to take place. These include;- wind, insects, birds, people etc.

Insects-pollinated flowers have scent, brightly coloured petals, produce sticky pollen grains / have sticky stigma.

Wind pollinated flowers produce a lot of pollen grains, have no scent, dull petals with no nectar.

LESSON 1       :       NON-FLOWERING PLANTS

Image result for non-flowering plants

Non-flowering plants are groups of plants that do not bear flowers.

Non-flowering plants are subdivided into three namely;

  • Spore producing.
  • Coniferous plants.
  • Algae
  • Spore producing plants are groups of non-flowering plants that reproduce by means of spores.
  • A spore is a single cell that can develop into a new plant under favorable conditions.

Examples of spore producing plants include; liverworts, mosses and ferns.

  • Ferns are the most advanced group of spore producing plants with proper leaves, stems and roots.
  • Mosses are small green cushion-like and grow commonly on house roof verandas, tree trunks, and in damp soils.
  • Liverworts have leaf like structures and commonly grow in wet moist places.

different examples of spore producing plants.

Fern Plant                                                                             Mosses Plant                                                               Liverwort Plant

    

Note:

All spore producing plants are green and therefore able to make their own food.

Coniferous plants are true non-flowering plants that do not bear flowers but reproduce by means of seeds protected in hard structures called cones.

Conifers have roots, stems and small needle shaped leaves

Examples of coniferous plants include

  • Pines
  • Cedar tree
  • Podo tree
  • Cypress
  • Fir tree
  • Ginko

Economic importance of conifers

  • Some are planted in compounds to provide shade and also act as wind breaks.
  • Some conifers are planted around the compounds and farmers to act as live fences

Algae 

These are simple plant like organisms which grow in water and in other dump places.

They differ from plants in that their cells are not clearly organized into tissues for a specialized function.

Examples of algae include;

  • Spirogyra, which looks like long green threads.
  • Sea weeds
  • Algae reproduce by cell division

A diagram of a spirogyra

NB: Green algae are found in a variety of habitats including fresh water, the sea, soil, tree trunks but the majority are aquatic.

 Uses of algae to people

  • Sea weeds like red algae can be eaten.
  • Sea weeds provide a number of important food additives
  • They also provide an agar used for growing micro-organisms
  • Algae are used in the production of biofuels.

LESSON   2      :       SEEDS

A seed is a mature fertilized ovule.

A seed develops into a young plant or a seedling under favourable conditions.

Seeds are classified into two;

  • Dicotyledonous seeds
  • Monocotyledonous seeds
  • Dicotyledonous seeds are seeds with two cotyledons

These seeds can be split into two equal parts of the cotyledons

Examples include:

  • Bean seeds
  • Peas
  • Groundnut seeds

All dicotyledonous seeds undergo epigeal germination.

 

A drawn structure showing parts of external and internal parts of a bean seed.

External Parts

Image result for external parts of a maize seed

 

 

 

 

 

 

Internal Parts

Related image    

A PRACTICAL ABOUT OBSERVING INTERNAL PARTS OF A SEED (BEAN/MAIZE GRAIN)

 

  • Monocotyledonous seeds are seeds with only one cotyledon.
  • They are mainly grains or fruits.

Examples include; maize, millet, sorghum, etc.

  • Monocotyledonous seeds undergo hypogeal germination.

Drawn structures showing external and internal parts of a maize grain.

Internal Parts                                                                                        External parts

Image result for external parts of a maize seedImage result for external parts of a maize seed

 

 

 

 

 

 

 

 

Seed coat (testa)Functions of the above parts.

  • It protects the inner delicate parts of the seed.

Cotyledon

  • Store food in the dicotyledonous seed
  • Absorbs stored food from the endosperm to the embryo during germination.

Endosperm

  • Stores food in monocotyledonous seeds.

Plumule

  • It grows into shoot system

Radicle

  • Grows into the root system.

Micropyle

  • Is a passage of air and water to the embryo.

LESSON 3       :       GERMINATION IN PLANTS

  • Germination is the development of a seed embryo into a seedling under favourable conditions.
  • During germination, the Radicle grows into the root system to support the seedling firmly into the soil.
  • The radicle also grows root hairs to absorb water and mineral salts from soil.

Types of germination.

There are basically two types of germination

  • Epigeal germination
  • Hypogeal germination

Epigeal germination is a type of germination where the cotyledon comes out of the ground.

Epigeal germination is a common characteristic of dicotyledonous seeds eg. Beans, soy beans, groundnuts.

Drawn structure showing the different stages in Epigeal germination.

Image result for stages in Epigeal germination

 

Hypogeal germination:

This is a type of germination in which the cotyledon remains under the ground

This type of germination is a common characteristic of monocotyledonous seeds.

Examples include; maize, millet, rice, sorghum etc.

Stages involved in Hypogeal germination.

Conditions necessary for seed germination.

  • A seed will only germinate under favourable conditions such as, oxygen, water and warmth.

Seed viability is the ability of a seed to germinate under favourable conditions.

A viable seed should be;

  • Mature and dry
  • Whole without a hole / wrinkles
  • Health and of a good variety

 

LESSON   4      :       FRUITS

  • A fruit is a mature fertilized ovary
  • A fruit is any structure in flowering plants that contains mature fertilized ovules.
  • A fruit has two scars i.e. style scar and stalk scar.

Fruits are divided into two;

  • Juicy fruits (succulent fruits)
  • Non juicy fruit (dry fruits)

Juicy fruits are groups of fruits with juicy pericarps and are eaten.

These include berries, pomes and drupes

Berries are fruits with many seeds like guavas, tomatoes, oranges etc.

Drupes are fruits with only one seed such as avocado fruit and mango fruit.

Pomes are fruits with few seeds like an apple.

Dry fruits

These are fruits whose pericarp is usually dry hard and woody.

They are divided into two namely;

  • Splitting (dehiscent fruits)
  • Non-splitting (indehiscent fruits)

Splitting fruits have capsule or pods that split to disperse their seeds when dry. E.g. Beans, peas and castor oil.

Non-splitting fruits have one seed only.

Their pericarp does not split to disperse the seeds but have structures for their mode of dispersal. Eg. Black jack, maize, sunflower, tridax etc.

Note:

  • Some fruits develop from one flower. They are called simple fruits.
  • Sometimes all flowers on a stalk make one fruit. Such fruits are called compound or multiple fruits Pineapple.
  • Some fruits are not formed from the ovary of a flower but from some other parts of a flower. Such fruits are called false fruits. E.g. an apple which develops from a receptacle

A PRACTICAL LESSON ABOUT THE INTERNAL PARTS OF A FRUIT (ORANGE & MANGO)

LESSON   5 :    SEED AND FRUIT DISPERSAL

Dispersal is the scattering of a seed or fruit from the mother plant to other area.

In some plants only seeds are dispersed while other plants it’s the fruits.

Importance of seed and fruit dispersal

  • Dispersal enables plants to colonize new areas
  • Dispersal reduces competition for light and the nutrients among plants.
  • Dispersal increases the chance of the plant survival.

Agents of seed and fruit dispersal

There are basically four agents or factors responsible for seed dispersal and these are;-

  • Animals, wind, running water and self mechanism

Types or mechanisms of seed dispersal are;

  • Wind dispersal
  • Animal dispersal
  • Water dispersal
  • Explosive mechanism.

Characteristics of seeds dispersed by animals

  • They are heavy and have juicy mesocarps
  • Some have hook-like structures to enable them attach themselves on the animals’ bodies
  • Some have hard seed coats to protect them from the digestive juices.

Examples of seeds dispersed by animals are;

  • Mango fruit
  • Guava fruit
  • Jack fruits
  • Avocado fruit etc.

Characteristics of seeds dispersed by wind

  • Many are small and light to be easily carried by wind.
  • Some like jacaranda seeds have wing-like structures for floating in air.
  • Some like a dandelion have a parachute hair structure

Seeds dispersed by self mechanisms split their pods when ripe and disperse their seeds.

These include; castor oil, peas and beans.

Seeds dispersed by running water are of plants that grow on water or near river banks.

Examples include;

Water lilies and coconut fruits.

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ASSIGNMENT : CLASSIFICATION OF PLANTS Assignment MARKS : 10  DURATION : 1 week, 3 days

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