Biology Lesson Note SS2 Third Term

Biology Topics for Senior Secondary school – Edudelight.com

THIRD TERM SCHEME OF WORK FOR SS2 BIOLOGY

OMEGA TERM SCHEME OF WORK FOR SS2

BIOLOGY

WEEKS	TOPICS
1	Respiratory System
2	Mechanism of Respiration
3	Aquatic Habitat (Marine)
4	Estuarine Habitat
5	Fresh water Habitat
6	Terrestrial Habitat
7	Forest
8	Grassland
9.	Ecology of Population
10	Food shortage
11	REVISION
12	EXAMINATION

ONE WEEK

TOPIC: RESPIRATORY SYSTEM

Respiration is defined as the oxidation of food substance in the cell particularly in the mitochondrion with the release of chemical energy, carbon(iv)oxide and water.

Characteristics of respiratory surfaces

1. Large surface area – this facilitate high rate of exchange gases.
2. Thin respiratory surface – this helps to shorten the diffusion distance.
3. Moist surface – thus enables the oxygen to dissolve before entering the blood or body fluid.
4. Permeability – the surface must be permeable so that oxygen and carbon(iv)oxide can pass through.
5. Well ventilated surface so that supply of oxygen to the surface are efficient
6. Efficient transport system or highly vascularised – this facilitates oxygen supply of the tissue. For example blood supply facilitates delivery of oxygen to carbon(iv)oxide from tissue.

Types of respiratory structures

1. Body surface: Gaseous exchange through the body surface is carried out by aquatic microscopic organisms using cell membrane e.g. Amoeba, Euglena. Some multicellular organisms such as earthworms, toad and frog carry out gaseous exchange through the skin (cutaneous respiration)

2. Cell Membrane: Microscopic aquatic organisms such as Amoeba and paramecium have no specialized organ for respiration oxygen intake and expulsion of carbon(iv)oxide is by diffusion.

3. Buccal respiration (month) frog or toad.

4. Gill respiration (fishes, crustacean, molluscs and tadpoles)

5. Tracheal respiration: all insects

6. Lungs respiration: reptiles birds and mammal.

QUESTIONS

1q.Mention the respiratory organs of the following  organisms

i. amoeba  ii .toad  iii. insects   iv. Earthworm

b.Outline  and explain the characteristics of a respiratory organ.

c. A  grasshopper respires by  means  of  its lungs.

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WEEK TWO

TOPIC: MECHANISM OF RESPIRATION IN LOWER ORGANISM

Oxygen intake and expulsion of carbon(iv)oxide in unicellular organism is by diffusion through the entire body surface.

Oxygen needed for respiration is dissolved in water. Based on the principle that molecular gasses will diffuse from a region of higher concentration to region of lower concentration, dissolved oxygen which is of higher concentration in water than in the cell will diffuse into the cell. After gaseous exchanges, carbon(iv)oxide which is now higher in concentration in the cell than in water will diffuse out of the cell into the water.

Exchange of gases takes place in the ectoplasm of unicellular organism e.g. Amoeba, paramecium and euglena.

Organisms	Respiratory surface	Functioning Environment
Amoeba & paramecium (unicellular)	Cell membrane	Aquatic
Molluscs, fishes, tadpoles and crustacean	Gills	Aquatic
Frogs, toads and earthworm	Tracheae	Terrestrial
Insects Reptiles, birds and mammals	Lungs	Territorial
Frog and toad Leaves Stem	Mouth Stomata Lenticels	Terrestrial Terrestrial Terrestrial

Mechanism of Respiration in insects

The respiratory organ in insect is the trachea system which is used for gaseous exchange. The insect has a tiny openings in their abdomen called spiracles through which oxygen diffuse into the body and CO2 diffuses out. The spiracle lead to a certain tube called tracheae which further divide into a smaller tube called tracheae and these tiny tubes are in contact with body tissues and body fluid.

Oxygen for respiration enter the abdomen and thoracic segment from surrounding atmosphere. The expansion of the abdomen cause the volume of the abdomen is increase thereby drawing air by diffusion into the body through the spiracles, tracheae, air sacs and trachioles. When the atmosphere oxygen reaches the fluid of the trachioles, it dissolves. The dissolved oxygen then diffuses into the tissues where cellular or tissue respiration. When the thoracic segments and abdomen contract, carbon(iv)oxide and water vapour diffuse from spiracles into the atmosphere.

Mechanism of respiration in fishes

The organ of respiration is the gills which are used for gaseous exchange. The gills are located of both sides of the head region. The gills which arranged in the gill chamber gills chamber. Each gill chamber is closed externally by operculum.

Gaseous exchange or breathing occurs across the gills surface. All the gills possess a very high surface area to volume ratio.

The fish opens its mouth and water rushes over the gills surface inside the opercula which are closed. As water flows over the gills, the dissolved oxygen in the water diffuses into the thin walled blood capillaries of the gills. At the same time, carbon(iv)oxide in the blood diffuses into the water. The alternate opening and closing of the mouth and opercula allow a constant flow of water over the gills. Oxygen is transported by the blood into every living cell where it is used for aerobic respiration. Hence, the gills are used for gaseous exchange or breathing and not for respiration.

Mechanism of respiration in Toad or Frog

1. Adult amphibians (toad and frog) breathe in three ways: through their skin (cutaneous breathing), through their mouth (buccal breathing) and through their lungs (pulmonary breathing).

Cutaneous respiration –The adult toad is capable of carrying out respiration using the skin both on land and in water. The toad skin is moist because it contains numerous glands which secrets a watery shine onto the surface so that gases can diffuse through it. The skin is also thin-walled and well-supplied with blood vessels to quicken the rate of diffusion of gases in and out of it.

Buccal respiration: The toad is capable of respiration by mouth when on land to serve as an efficient respiratory organ. To breathe with the mouth, the mouth is closed, the nostrils are opened and the buccal cavity floor is lowered by muscular action. The buccal cavity volume increases, its air pressure decreases and air is drawn through the nostrils. Oxygen in the air diffuses into the lining of the buccal cavity which is well-supplied with blood capillaries when the nostrils are used. In exchange, CO2 from the blood capillaries is given off by diffusion. The buccal cavity floor is raised, its air pressure increase and so air containing a lot of carbon(iv)oxide and water vapour is expelled through the nostrils.

Lungs or pulmonary respiration: The toad and frog uses their lungs for breathing only on land when it is very active and demand for oxygen is high. Air is drawn into the buccal cavity and the nostrils are closed. The buccal cavity floor is raised and air is expelled through the larynx into alveoli of the two lungs in which gas exchange occurs. The alternate raising and lowering of the buccal cavity ensures that air is forced into and out of the lungs. Air is expelled through the nostrils when they open, while the contraction of the lungs also aids the sending out air.

Respiratory system of man

The respiratory system in man includes the nasal passage or nostrils, pharynx, larynx or voice box, trachea or windpipe, bronchus, bronchioles and alveoli. The nostrils lead into the posterior position of the mouth cavity called pharynx and this leads into voice box or larynx. The larynx leads into the windpipe or trachea. A flat piece of tissue called epiglottis cover the entrance to the larynx and trachea when swallowing food. The trachea branches into two bronchi. Each bronchus leads to the lungs where it branches into small tubes called bronchioles. The bronchioles lead to numerous air sac called alveoli.

The alveoli are richly supplied with blood capillaries and are sites or surface where gaseous exchange takes place.

Mechanism of respiration in man

The mechanism of breathing in mammals involves two phases. These are external and internal respiration.

External respiration or breathing is defined as the exchange of gases between the environment and the respiratory organ of the living organism. External respiration involves two processes inspiration or expiration.

INSPIRATION OR INHALATION: This is the breathing in of oxygen into the lungs. The followings take place during inspiration.

1. The thoracic cavity first increases in volume
2. The diaphragm contracts and becomes flattened
3. The intercostal muscles contract
4. The sternum move forward
5. The ribs are moved upwards and outward
6. The thoracic cavity increases in volume but the pressure decreases, air from outside is drawn into the lungs or alveoli through the nose, trachea, bronchi and bronchioles leading to an increase in the size of the lungs.

EXPIRATION OR EXHALATION: This is the breathing out of CO2 and water vapour into the atmosphere or environment. The following processes takes place during expiration.

1. The thoracic cavity first decreases in volume
2. The diaphragm relaxes and assume its dorm shape.
3. The intercostal muscles relax
4. The sternum moves inward
5. The ribs are moved downward and inward.
6. The thoracic cavity decreases in volume and the pressure increases, this cause air containing waste products like CO2 and water vapour from inside alveoli of the lung to be forced our through bronchioles, bronchus, trachea and finally to the outside through the nose.

Internal / Tissue / Cellular respiration is defined as a chemical activities of the cells in which glucose is broken down using oxygen by a series of reactions controlled by enzymes to release energy. The energy released is stored in adenosine triphosphate (ATP).

ATP is the form in which energy is carried, stored and used by all living cells for various metabolic activities.

The lungs occupy the thoracic cavity from the shoulder to the diaphragm. It overlaps the heart. It is spongy and surrounded by an elastic membrane called pleural membrane which allows stretching.

Mechanism of gaseous exchange in leave

The green plants respire along with photosynthesis during the day light. During respiration, plant take in air form their surroundings, use the oxygen of the air to breakdown stored food for the purpose of energy production and release carbon(iv)oxide and water.

In simple aquatic plant such as spirogyra, dissolved air/oxygen in water diffuses into the cells through the general body surface but in vascular or higher plant atmospheric air enters through stomata of the leaves and lenticels of the stem through the process of diffusion. Due to differences in concentration gradient, oxygen is taken in through the stomata and lenticel especially during the night and CO2 and water are given out.

But during the day, when photosynthesis is going on, oxygen and vapour from photosynthesis diffuse out to the exterior through the stomata and lenticels. The opening and closing of the stomata is controlled by the guard cells. Turgidity of guard cells quicken the opening stomata while the flaccidity of the guard cell cause the closing of the guard cells.

Oxygen debts is defined as the quick breathing to take oxygen to the muscle cells lacking oxygen in other to oxidize the lactic acid build up in the muscle.

 (Causes of oxygen debt OD)

1. Vigorous exercise leading to shortage of oxygen in muscle cells
2. Lungs unable to meet the demand of oxygen in the cell of muscles
3. The cells of the muscles have to respire aerobically producing lactic acid little energy.
4. Lactic acid accumulation in the muscle cells
5. After vigorous exercise, the lactic acid remains in the muscle cell resulting in muscle fatigue and aches
6. More oxygen is then required to repay the debt of oxygen in the muscle cells.
7. When sufficient oxygen is breathed in to oxidize the lactic acids, the debt has been paid.

          QUESTIONS.

1a.The respiratory organ found in the cockroach is A. air sac  B. trachea  C. lung book. D. gill

2.The movement of diaphragm is characteristics of mammal of gaseous exchange in  A. insect B. fish C. road .D.  mammal

3.In cellular respiration, energy is stored the form  of A. adenosine triphosphate B. adenosine diphosphate  C. adinosine monophosphate  D. heat energy.

4.Which part of  the gills of a fish is involved in gaseous exchange ?A. gill slits B. gill beers C. gill filaments D. gill scale

5.Which of the following is not  a product of fermentation of glucose? A. energy B.  alcohol  C.  carbon dioxide D. lactic  acid.

7.Gaseous exchange in Aves  occurs in the A.  tracheas B. bronchi C. air sacs D. trachea.

Theory

8a.What is external respiration?

b. List the structures involved in breathing in mammal

c. Make a large labeled diagram of mammalian respiratory system of man

d .What is oxygen debt? Explain the causes of oxygen debt.

e. Explain the following  i. inspiration  ii expiration   iii .internal respiration.

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WEEK THREE

TOPIC: MARINE HABITAT

Marine habitat is made up of the shore and open sea which are water that is extremely salty. It has the characteristic that influenced the survival of organism.

Characteristic of marine

1. It has high salinity i.e. high salt concentration pressure increases with depth
2. Temperature decreases with depth
3. It has very low concentration of dissolved nutrients
4. The sea water is continuous movement caused by the wind.
5. They are moved by waves and tidal current
6. The density is higher than fresh water
7. The pH of the surface water is alkaline
8. The turbidity of the ocean water is high due to the suspended particles washed into it from land and river.

The marine habitat can be divided into the intertidal, littoral and occanic zone.

(A) INTERTIDAL ZONE: It is a zone that is covered with water during high tide and with air during low tide period. It is rich in organic matter and dissolved oxygen. The water is constantly in motion.

The organisms that are present there are limited to borrowing organisms like grabs, snails, periwinkles, worms auger, shell, gastropods, barnacles, oyster, mussel and limpets having adhesive structures found at the rocky shore.

Plant such as green algae, red algae are there

Adaptation of the organisms

The organisms have several adaptive features used to avoid drying out some like to borrow in the soil with their feet, some gothics and shells. Some animals like anemones withdraw their tentacles and fill their body cavity.

(B) LITTORAL ZONE (NERITIC ZONE) – This zone extends from the shoreline to the edge of the continental shelf where the depth of water is about 200m. Due to deep nature of the water, there is reduction in waves and tidal distribution. The zone is rich in free floating and bottom dwelling algae that serve as primary producers for varieties of plant eating animals. The distribution of the organisms is based on factors such as temperature, water, salinity, turbulence and lighting. The zone is the main site of commercial fish harvest because the zone is very rich nutrients. Fishes like mackerel, cod, herring, salmon etc.

(C) OCEANIC ZONE (APHOTIC ZONE): is zone of deep water that stretches beyond continental shelf. The zone is quite unproductive because raw materials required for photosynthesis are not sufficient. Although, there is enough light at the water surface, nutrients are inadequate and the dark. The zone support the growth of minute floating plant and animal planklon. They are usually unicellular algae, protozoans, small crustaceas and larvae of invertebrates.

The adaptive features include oil globule in their body that acts like float possession of external spines and air which provide friction and prevent drowning. The producer plankton (diatoms) and algae (sea weeds) sustain all the marine food chain which sustains all other life forms in the marine habitat.

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WEEK FOUR

TOPIC: ESTUARINE HABITAT

An estuary is the point where a big river enters the ocean. This habitat is created by the mixing of fresh water and salt water because of tidal action. Here, salt water from the ocean mixes with fresh water from the river  to form an intermediate water known as brackish water. The salinity of ocean flunctuates with distance from the dry and rainy season.

Characteristics of Estuarine

1. The water is brackish that is the salinity is intermediate between freshwater and salt water.
2. The volume of water rises with high tide and falls with low tide
3. The habitat is flooded and exposed as the tide rises and fall
4. The bottom is made up of soft mud
5. There fluctuation in salinity and temperature
6. It has rich and highly productive soil owning to the high deposit of alluvial soils
7. There is usually no wave action

Adaptive features of estuarine water plant and animals

1. Animals have body fluids of equal concentration as that of the surrounding water, making them to tolerate change in salinity
2. Some of the animals have adaptive features that aid in attaching firmly to rocks, while some hide in rocks, crevices to protect themselves against wave action.
3. Plants that grow in estuarine are red mangrove, white mangrove and raffia palm
4. Animal found in the mangrove swamp include fishes, mud skipper, barnacles and oysters
5. Plants and detritus as primary producer that sustains other life forms in the habitat spearhead

•  the food chain in estuarine habitat.

Detritus                           Shrimp                        Fish                     Bird

Animals such as shrimps, crabs and snails are eaten by higher members especially fish and birds.

Types of Estuarine

1. Tidal marsh or embayment
2. River mouth

QUESTIONS.

1.An aquatic habitat that is not moving is  A. lotic  B.lentic  C.bentic   D.netic

2.Epiphytes are usually found in ……………….. habitat

A. desert  B. forest  C.marshland  D. grassland.

3.The driest habitat is  A. desert  B.fotest  C. savannah  D. swamp

4.The largest and  deepest aquatic habitat among the following is  A . oceans  B.seas  C.lake   D. river

5.Which of the following is a xeromorphic plant? A.cactus  B.watre leaf  C.water lily  D.balsam plant

THEORY

6. What is marine habitat?

7.Mention any four aquatic  habitat

b.Outline the characteristics of marine habitat and discuss any four of them.

WEEK FIVE

TOPIC: FRESH WATER HABITAT

Fresh water are all inland water bodies which are salt-free or contain no significant amount of salt.

Types of salt

1. Lentic habitat – are standing or stagnant water bodies such as the ponds, lakes, pools and standing swamps.
2. Lotic habitat – are free running or flowing water bodies such as rivers, springs and streams.

Characteristics of fresh habitat

1. It has low concentration of dissolved salts
2. It has varying oxygen level and light intensity that depends on water depth
3. It has a fluctuating temperature
4. It has extremely low salinity
5. The animal may be affected by the relent of the water
6. Current of the water may be high.

Zones of freshwater habitat (lake)

A lake consists as example of freshwater habitat has three main zones.

1. LITTORAL ZONE: This is the shallow water region in which sunlight penetrates to the bottoms. The producers in the zone are of two types: rooted species that are mostly plants examples water lettuce, duke weeds, water lily, water hyacinth.

The other category of producers are phytoplankton must of which are algae. Such plants are used for food and shelter by amphibious animals and aquatic insects which spend part of their live in the pond or lake.

2. LIMNETIC ZONE: This is the open water zone extending to the depth of effective sunlight penetration. The zone consists largely of phytoplankton producers and algae like green flagellates e.g. Euglena. The most abundant vertebrates in the lake are fishes which spend must of their time in the littoral zone though they move freely between the littoral and limnetic zone. Certain birds visit the lakes to feed on worms, small fishes and mollusks’. Example of such birds are herons, storks, flamingos. The most important animal of this zone is the fish.

3. PROFUNDAL ZONE: This consists of the bottom and deep water area beyond the depth of effective sunlight penetration. The profound zone is not often found in ponds because they are not usually as deep as the lakes. Since light penetration is pour in this zone, the organisms depend on the limnetic and littoral zones for basic food substance. The animals that are found here have adaptation to withstand periods of low oxygen concentration. Oxygen and light are therefore factors that limit existence of organisms.

Adaptive features of freshwater animals

1. Possession of elongated bodies with airs or flattered appendages to enhance buoyancy in water
2. Possession of streamlined bodies by mobile organisms to reduce resistance in water e.g. fishes
3. Possession of adhesives features like hook, sticky under surfaces, suckers by stationary organisms to enhance attachment.
4. Possession of adaptive features like hacmoglobin in the blood of the hookworms extensive breathing tubes and other that enable them to survive in oxygen poor environment

Adaptive features of freshwater plants

1. Possession of porous tissues (e.g. water lettuce) or reduced bodies e.g. (Azolla) to enhance
2. The leaves of submerged plant are thin and divided to allow more surface area for light absorption in the depth of water and reduce resistance to water flow.
3. Possession of hairy roof that are shorter and less branched because they are needed for absorption only and not for anchorage
4. Possession of long and flexible submerged items that allows swaying with water current.

QUESTIONS

1. Write on the followings
2. Estuarine habitat
3. Marine habitat
4. Fresh water habitat
5. List 5 characteristics of fresh water
6. List 3 adaptive features of a, b, and c above

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WEEK SIX

TOPIC: TERRESTRIAL HABITAT MARSHES

Terrestrial habitats are described mainly by the types of vegetation they have and that

vegetation depends on the rainfall and temperature. The first terrestrial habitat is a marsh.

A marsh is a low, flat land completely or partly covered by shallow water with silt frequently

deposited. Marsh is thickly covered by stiff water grasses, tree are absent but birds and

insects are common.

Characteristics of the Marsh

i. The soil is always covered with water (water egged)

ii. The water and soil are poorly aerated as dissolved oxygen is constantly being

used by micro-organism (bacteria and fungi) for decay.

iii. The land is low lying and flat

iv. The vegetation is mainly stiff water grasses and other herbs

v. The water is usually shallow

vi. Light penetration is low because of decaying organic matter in suspension

vii. The fauna is dominated by water birds, insects and water snakes.

viii. It has high relative humidity

ix. Nutrients and remains of organic matter always accumulate making it to be

highly productive.

Formation of Marshes

Marshes are formed by water flowing into a flat lowland from a flooded river. The clay soil

holds the water while the vegetation cover of grasses and lilies help to reduce evaporation.

Marshes may also be formed by gradual accumulation of debris or sediment of plant,

animal remains and deposit from streams and rivers entering a lake or pond. Subsequently,

plant such as grasses and lilies are introduced with water bird, aquatic insects and water

snakes.

Types of Marshes based on life span

i. Temporary marshes are seasonal, occurring during the rainy season and drying

up in the dry season.

ii. Permanent marshes contain water throughout seas which serves as permanent

water source.

Types of Marshes based on composition

i. Fresh water marsh: populated by algae, plants like water lettuce, sword grass

and animals like toad and fishes.

ii. Salt water marsh: populated by algae, plants like grasses and sedge, and animals

like crabs, oyster, barnacles and mud skipper

Adaptive features of animal in Marshes

i. Worms, crabs and bivalves burrow into the soft mud to avoid high temperature

and drying up.

ii. Insect larvae, beetles and frogs come near the surface from time to time to gulp

atmospheric air to survive the low oxygen content in the water.

Adaptive features of plants in Marshes

i. The grasses grow in large bunches or tussocks to avoid being washed away by

water movement.

ii. The leaves are long, narrow and held high above water for atmospheric gaseous

exchange to compensate for floor aeration of the water-logged soil.

iii. The algae salvina, azolla and duckweed are on the surface to receive both

atmospheric and dissolved oxygen to meet their oxygen requirement

QUESTIONS

1a.Name one plant and one animal that are found  in each of the following habitats  .i   fresh water pond  ii.tropical rainforest  iii. savannah

b.State how the named plant and animals are adapted to each of the habitats.

. WEEK SEVEN

TOPIC: FOREST

Terrestrial habitat are environment consisting of ground on earth such as forest, grassland,

uncultivated land and a fellow farmland.

FOREST

A forest is communities of plant dominated by fall trees that branch at top and provide a

thick canopy. The interior of forest is characterized by high humidity, low light intensity, still

air and damp floor.

Characteristics of Forest

i. It is usually found on soil that is not water logged

ii. It is characterized by high temperature of 27 0 0C

iii. A relative humidity of about 70%

iv. It has a mean annual rainfall ranging from 2000mm – 4000mm

v. The heights and canopies of the trees determines its structure

vi. The common plant in the forest are epiphytes and woody climbers.

Forest stratification

Strata are layers of vegetation present in the rain forest. These layers are as follows:

1. Upper layer is made of giant and tall trees of about 40m – 60m forming canopy over the

middle layer. The trees in this layer enjoy the best of sunlight e.g. Mahogany is an example

of giant tree. Animal leaving there are flying birds such as eagles, parrot and vulture.

2. Middle layer – This consist of tall trees of about 33m forming a continuous canopy. These

trees form canopy have long slender trunks and rounded crowns. The trees are bound

together by large climbing and creepers. Forest birds such as parrot, owls and other animals

such as bat and monkeys are there.

3. Lower layer – It consists of trees of height 10m – 15m. It is dense except for some break in

the canopy dew death of a big tree. Animals living there include monkeys, snakes, lizards,

tree-frogs.

4. Shrub layer – These are plants that are small and fully grown. Their leaves are large with

colourful flowers.

5. Forest Floor – This layer consist of herbs, ferns and fungi. There are also numerous

climber and epiphyte and mobels.

6. The climbers consist of plants which are rooted on the ground but need support for their

weak stem.

7. Epiphytes – These are more or less short stemmed plants, intolerant of the conditions at

the ground level, so they grow roots on the stems and branches of other plants.

WEEK EIGHT

TOPIC: GRASSLAND

Grassland or savannahs are land which are covered with grasses weather high or short

grasses. It occurs where the annual rainfall is low and vegetation consists of majority of grasses

with shrubs and trees. Climber and epiphytes are absent.

Distinctive features of the grassland

i. Low rainfall

ii. Dry and hot environment

iii. Long dry season

iv. Populated by larger animals like giraffe, antelope, hyena, lion, leopard and zebra.

Animal Adaptations in Grassland

i. Nutrient adaptation as most animals feed on grass or grass past

ii. Fast moving large herbivores like zebra with good eye sight

iii. Fast moving large herbivore can also detect predator and run in an open habitat

iv. The animals are tree to run with any hindrance.

Plant Adaptation in Grassland                                                       

i. Most plant set and disperse their fruits in the dry season because they are adapted to wind pollination

ii. Possession of waxy surface and hairy leaves by plant reduce transportation this unable the plant to survive dry wind.

iii. Leaves are shed by the trees in the dry season to conserve water

iv. Possession of bark insulate the trees from fire damage

v. Several plants possess underground stem that are adapted to seasonal drought

vi. Many plants have deep penetrating roots to search for water.

ARID LANDS

These are habitat that is associated with dryness or aridity. They are dried habitats. It is

divided into:

i. Tropical desert

ii. Warm temperate desert

iii. Cold desert (Tundra)

Features of a tropical desert

i. It is characterized with a temperature range of 27 0 C to 35 0 C in the summer and

15 0 C in the winter

ii. It has a very hot and cold night due to absence of clouds

iii. It has absolutely low rainfall

iv. Wind erosion occurs due to soil dryness

Features of cold desert (Tundra)

i. It is characterized with long days of a short summer period with temperature of

about 10 0 C

ii. It characterized with muddy water logged soil

iii. Very cold, long dark winter that freeze lakes and rivers and hardened the

ground soil due to the freezing of the soil moisture.

iv. Annual rainfall is about 250mm

Sahara Desert (Hot)

Distinctive features

(i) Mean annual rainfall is less than 100mm

(ii) It has extreme dryness, winds, high temperature during the day and cold, night.

(iii) Poor, sparse vegetation, plant are mostly ephemeral herbs and succulent e.g.

cactus.

Plants that are adapted to dry habitats are called Xerophytes and have the following

characteristics.

i. It has elongated slender stem, branching root capable of penetrating great

depths.

ii. Possession of water storage tissue in their stem

iii. Possession of adaptive feature as waxy leaf with water proof cuticle, sunken

stomata with air and thick layer over the stem and root.

Adaptive feature of Animal in the Avid Land

(i) Body covering is dry and impermeable is water

(ii) Engage in burrowing during the day and active in the night to avoid the day heat.

(iii) Possession of excretory system to reabsorb water efficiently.

(iv) Possession of membranes that reduces water loss with exhale air.

(v) Possession of fringed feet and toes that enhance walking on loose sand.

(vi ) Possession of sandy coloured body to aid camouflage and  remain undetected

.

WEEK NINE

TOPIC: ECOLOGY OF POPULATIONS

Ecological succession is a chain of events in which one community is gradually replaced by

another in an orderly series, until a suitable community climax which is best adapted to the

environment is established. The terminal climax community is a state of stability with the

ecological conditions existing within the locality.

General characteristics and outcome of succession.

i. Succession brings about greater species diversity, greater species population

density and large life form.

ii. Succession is predictable and occurs along one direction in the ecosystem

iii. As communities are constantly undergoing changes. It shows that the biosphere

and ecosystem are dynamic

iv. Succession is caused by the modification of physical environment by the

community itself.

v. Ecological successions show that some organisms are more easily dispersed and

are more vigorous and grow more rapidly than others.

vi. Succession occurring in different places and at different times involved are often

different

vii. Climax communities are formed after a long period of time and once formed

they maintain their structures.

viii. Succession makes the food web become more complex and the relations

between the species become better defined or more specialized.

ix. The amount of inorganic nutrients held by the organisms and soil of the

ecosystem increases

Types of Succession

1. Primary Succession is a type of succession that occurs on a bare surface where no

Community of plant existed before it involves the formation of new soil. It begins from

(a) Dry rock slope which eventually changes to a forest

(b) Shallow lake gradually filled up with vegetation to become a marsh and eventually a

forest.

(c) Mouth of a river where silt or mud is deposited thereby forming a bank on which a

mangrove swamp develop and eventually a tropical forest.

2. Secondary Succession is a succession or changes on a surface that already or previously

has a community of plant to be replaced by another. For instance changes occurring on (i)

overgrazed grassland (ii) abandoned farm land.

CLIMAX COMMUNITY

A climax community is the end product of the succession of several seral communities over

a long period at one place. Once climax community is established it may remain indefinitely.

The climax community is regarded as steady state which has restored the community

structure towards steady state.

Characteristics of a stable ecosystem or climax communist

i. It is generally believed that once the climax is attained, the community does not

change at all. Climax community changes due to aging and it is heterogeneous

ii. The climax community depends on the broad climax of the region

iii. Climax ecosystem has numerous micro-habitat which are inhabited by different

types of organisms.

iv. Climax community does contain many sub-communities.

OVERGROUNDING

Over-grounding is defined as a situation which occurs when a population in a given habitat

Increases beyond a point where the resources in the habitat such as space and food are not

Enough to support the individual in population.

Factors responsible for over-grounding

i. Limited space

ii. Increase in birth rate

iii. Limited food supply

iv. Flux of immigrants

v. Less emigration

vi. Decrease in mortality rate

vii. Increase in survival rate

viii. Barriers

Effect of over-grounding

i. Shortage of space

ii. Shortage of food

iii. Competition

iv. Anti – social behaviour

v. Spread of diseases

vi. Preying on each other

vii. Death of the organism

Adaptation to avoid over-grounding

1. Territorial Behaviour – is an act in which an organism defend an area or a territory against

an intruders especially in animals lizards, birds.

2. Dispersal of seeds and fruit – the disposal of seeds and fruit either by water, winds,

Animals, insect and explosive mechanism reduces the chance of over-grounding.

3. Emigration is the movement of organisms away from habitat or a particular locality.

4. Swarming – it contain insects such as termite and bees to form new colony is a way of

decongesting the population.

5. Production of chemicals by plant as this prevent the growth of plants sometimes prevent

the growth of other plants.

6. Production of canopies by tall trees which prevent the trees underneath from growing.

QUESTIONS

1a.What is climax community

b. Discuss briefly the various stages starting with a bare rock to a climax community

2a.Define succession

b. Describe a succession in a pond or abandoned farmland

c.State some effect of over-crowding.

WEEK TEN

TOPIC: FOOD SHORTAGE

Food shortage simply means non availability of food or scarcity of food to support the existing  population or an individual.

Causes of food shortage

i. Over-population

ii. Poor storage facilities

iii. Natural disaster such as flood or volcanic eruption

iv. Drought

v. Pest and diseases

vi. Bush burning

vii. Poor harvest

viii. Infertility of the soil

ix. War

x. Inconsistency in government policies

Effects of food shortage

1.It may lead to malnutrition which reduces their reproductive capacity.

ii. It  leads to bearing of weak and inactive off springs.

iii. The center food chain and food web may be affected.

iv. It leads to emigration

v .It leads to completion

vi .It increases the rate of mortality.

Factors  Affecting  a Population,

The factors that may limit the growth or increases the natality or mortality rate or  emigration  rate of population are grouped under the term Environmental Resistance which is also divided into  Density Independent and Density Dependent factors. The density of a population is simply the number of individual in a given unit of an area at a particular time. These are Biotic and Abiotic factors .Abiotic factors includes light, temperature,  heat, edaphic ,precipitation, altitude and latitude.

Biotic factors include  presence or absence of their species, their death , their birth rate, completion ,dispersals, emigration and immigration. Temperature is for an example of a density independent factor while food is density dependent factor

QUESTIONS

1a..Define the term population

b.List two biotic abiotic factors each that affect population growth

c. What are effects of food shortage on a  population?