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1. Ecology
Biology Notes
GCE Study Buddy

2. Ecology
●Ecology is the study of interactions among organisms,
and between organisms and the physical and chemical
factors making up their external environment
●Ecologists study both the non-living (abiotic) or physical
environment, and the living (biotic) environment.

3. Physical environment
●Amount of light
○Light intensity affects the distribution and growth of both plants and
animals
●Amount of water
○Xerophytes are plants which can live in conditions of prolonged
drought in their habitat
○Plants which live in water or very wet places are called hydrophytes
○Pneumatophores arise from the root system and project above the
surface
●Temperature
○Within a certain range, a fall in temperature usually results in a
decrease in the metabolic activities of the organisms
●Salinity and pH of the soil or water
○The salt concentration of the cytoplasmic contents of freshwater
organisms is usually higher than that of the surrounding water so that
water tends to enter these organisms by osmosis
○Aquatic organisms are sensitive to the effects of the pH of the water

4. Biotic environment
●Habitat: the place where an organism lives
●An organism in any habitat is never an independent unit.
○Its daily existence depends on and is influenced by other organisms around
it
●Ecological niche: the function of an organism or the role it plays in the
habitat is known as the
●Population: a group of individuals of the same species occupying a
given area – expressed in terms of density (number of individuals per
unit area)
○Population increases when the number of new individuals added to it
exceeds the number lost through death or migration and vice versa
●Ecological unit: when different populations of plants and animals live
together and interact within the same environment
●Ecosystem: an ecological system formed by the interaction of living
organisms and their non-living environment (both biotic and abiotic
factors)

5. Ecosystem

6. Organization levels in ecology

7. Ecosystem
●In any ecosystem, the living organisms can be identified as
producers, consumers or decomposers
●Producers: mainly green plants that manufacture complex organic
food substances from raw materials
○They are the only organisms that can convert radiant energy into
chemical energy and store it in their food molecules during
photosynthesis
○Producers affect the lives of other organisms because they are the
beginning of a food chain
●Consumers: obtain their energy from other organisms on which
they feed. Animals are consumers
○herbivores feed directly on plants (primary consumers
○Carnivores feed on herbivores (secondary consumers)
●Decomposers: act on dead organisms and enable the materials
locked up in them to be returned to the physical environment and
be used again by green plants

8. Food chain and food web

9. Food chain and food web
●Each stage in a food chain is known as a trophic level
●A predator is an animal that feeds on another animal
called prey
●Food chains are linked up together to form a food
web or food cycle

10. Ecological pyramids

11. Ecological pyramids: pyramid
of numbers
The number of
organisms at each
trophic level can be
used to construct a
pyramid of numbers

12. Ecological pyramids: pyramid
of numbers
●Variation in pyramid of numbers
○Pyramid of numbers may be inverted if organisms of one
trophic level are parasitic on organisms of another trophic
level

13. Ecological pyramids: pyramid
of biomass
Biomass is the total mass
of living matter in each
trophic level at any one
time

14. Ecological pyramids: pyramid
of energy
●A lot of energy is lost to the
environment as food is transferred
from one trophic level to the next
●The total energy level decreases
progressively along the food chain
●Therefore, the pyramid of energy is
always broad at the base and
narrow towards the apex
●Energy may be lost to the
environment
○As heat during respiration at
every trophic level
○Through undigested matter
egested by consumers
○Through excretory products eg

15. Ecological pyramids: pyramid
of energy
●The greatest amount of energy is lost during its transfer
from producer to primary consumer
●The progressive energy loss explains why food chains
are generally short
○A shorter food chain means more energy is available to
the final consumer

16. Non-cyclic energy flow in the
ecosystem
●In any ecosystem, the ultimate source of energy is the sun
●The flow of energy through the ecosystem is non-cyclic eg
energy released as heat to the environment does not return
to the same system or organisms that produced it
●Dead parts and bodies of organisms and egested and
excreted materials contain trapped chemical energy
○This is finally released by the activity of microorganisms which
use some of this energy for their needs while the rest is lost as
heat
●Eventually, all the energy that enters the biotic part of the
ecosystem is lost as heat energy

17. Carbon Cycle
●Living organisms need carbon to:
■make food (green plants photosynthesise)
■make energy (through respiration)
■make new cells for growth and repair
●Carbon cycles through ecosystems, moving repeatedly from one organism to
another, and between organisms and the environment.
●The various processes by which carbon, in the form of carbon dioxide, is
removed and restored to the atmosphere constitute the carbon cycle
●During photosynthesis, green plants absorb carbon dioxide from the
atmosphere and use it to manufacture carbohydrates (glucose)
●Glucose may be changed to other organic compounds like fats and amino
acids or proteins
●When animals feed on green plants, the carbon compounds become part of
the bodies of these animals
●The carbon compounds may be preserved in fossil fuels

18. Carbon Cycle
●Release of carbon dioxide into the atmosphere
○Respiration: when living organisms respire, carbon
compounds like glucose are broken down and carbon
dioxide is released into the environment
○Combustion: burning of fossil fuels, like coal and natural
gas, releases carbon dioxide into the atmosphere
○Decay: when organisms die, their dead bodies are broken
down into simple organic and inorganic substances by
decomposers (bacteria and fungi)
■Some of the simple organic matter released during decay is
absorbed by decomposers and becomes part of their bodies
■When the decomposers respire, carbon dioxide is again
released into the atmosphere

19. Carbon Cycle
●Importance of carbon cycle
○Ensures that there is a continuous supply of inorganic
carbon dioxide for plants to carry out photosynthesis – a
process that converts solar energy into chemical energy
(food) which other non-photosynthetic organisms can use
to stay alive
○Enables a linear flow of energy through the ecosystem.
The carbon compounds are the vehicles through which
the trapped solar energy passes from organism to
organism in the food chains of an ecosystem

20. Carbon Cycle

21. Nitrogen Cycle
●Living organisms need nitrogen to make proteins. They
cannot get it directly from the air because nitrogen gas
is too stable to react inside an organism to make new
compounds.
●Nitrogen must be changed into a more reactive form to
allow plants and animals to use it. Plants can take up
and use nitrogen when it is in the form of nitrates or
ammonium salts. Nitrogen fixation is the process when
it is changed into a more reactive substance.

22. Nitrogen Cycle

23. Parasitism
●Parasitism is an association between two organisms such that one organism
(parasite) lives on or in the body of another organism (host)
●The parasite derives its nutrients, and usually shelter from its host. In this
process, it normally does some harm to its host
●Malarial pathogen
○Malaria is a disease that is endemic in many tropical countries
○Caused by certain species of Plasmodium – a parasitic protozoan that spends one
part of its life cycle in Man and the other part in the female Anopheles mosquito
○Malaria is transmitted by the female Anopheles mosquito – a vector is an organism
that carries disease-causing organisms and transmits disease
○Signs and symptoms
■Intermittent fever every 48 or 72 hours
■Malarial parasite attacks liver cells and red blood cells
■The toxin causes fever, usually accompanied by chills, shivering, and profuse sweating
■Death may occur if untreated

24. Life cycle of Anopheles
mosquito
Egg : Eggs are laid one at a time and they float on the surface of the water.
Anopheles species do not make egg rafts but lay their eggs separately. Anopheles
lay their eggs on water. Most eggs hatch into larvae within 48 hours.
Larva : The larva (larvae - plural) live in the water and come to the surface to
breathe. They shed their skin four times growing larger after each molting. Most
larvae have siphon tubes for breathing and hang from the water surface. Anopheles
larvae do not have a siphon and they lay parallel to the water surface. The larva feed
on micro-organisms and organic matter in the water. On the fourth molt the larva
changes into a pupa.
Pupa: The pupal stage is a resting, non-feeding stage. This is the time the mosquito
turns into an adult. It takes about two days before the adult is fully developed. When
development is complete, the pupal skin splits and the mosquito emerges as an
adult.

25. Life cycle of Anopheles
mosquito

26. Control of malaria
●Treating infected persons with drugs to kill the
pathogen
●Uninfected persons taking preventive drugs if they are
travelling in malarial regions
●Using a knowledge of the vector’s habits and life cycle
to get rid of their living and breeding places