Biology

1. The Nature and variety of Living Organism

Pathogens

Characteristics of Pathogens

General Properties

 Pathogens are microorganisms that can cause disease in their host.

 They include several types of organisms such

as bacteria, viruses, fungi, and protozoa.

 While many microbes live harmlessly in and on the human body,

pathogens are those which can cause harm or illness.

Transmission of Pathogens

 Pathogens are often transmitted via the air, through direct

contact, contaminated food or water, or via vectors like
mosquitoes.

 They are able to move from one host to another using these methods,
causing infections and illnesses.

Impact on the Host

 Pathogens have various mechanisms to infect the host and cause

disease, including by producing toxins, invading tissues, or triggering
an overreaction of the immune system.

 The severity of the disease can vary greatly, from mild conditions to
severe, life-threatening illnesses.

Types of Pathogens

Bacteria

 Bacteria are unicellular microorganisms and can be pathogens,

causing diseases such as tuberculosis, bacterial pneumonia or cholera.
  They can be treated with antibiotics, though antibiotic resistance is an
increasing problem.

Viruses

 Viruses are smaller than bacteria and invade the host’s cells to
replicate. They are responsible for diseases like influenza, HIV/AIDS and
COVID-19.

 Antiviral medications can help manage viral diseases, but cannot

always eliminate the virus completely.

Fungi

 Fungi are eukaryotic microbes that include yeasts and molds. Some
are pathogenic and can cause diseases like ringworm or thrush.

 They can often be treated with anti-fungal drugs, though some

infections can be more serious.

Protozoa

 Protozoa are unicellular organisms often transmitted through water.

They can cause diseases such as malaria or sleeping sickness.

 Anti-parasitic treatments are used to manage protozoan infections.

Response to Pathogens

 The human body has a complex immune system that fights against
pathogens, getting rid of many before they can cause disease.

 Vaccination can help prepare the immune system against certain

pathogens, providing immunity to serious diseases.

Roles of Pathogens

 While pathogens are often harmful, some play beneficial roles, such as
aiding in digestion or boosting the immune system.

 Understanding pathogens and the body’s response to them is a crucial

part of biomedical science and disease management.
Prokaryotic Organisms
Characteristics of Prokaryotic Organisms

General Properties

 Prokaryotes are simple, unicellular organisms forming another

essential group of living organisms.

 The term Prokaryotic indicates organisms whose cells lack a nucleus

and other membrane-bound organelles.

 Bacteria and archaea are the two domains that make up prokaryotic
organisms.

Cell Simplicity

 Prokaryotic cells are typically smaller and simpler than eukaryotic

cells.

 They lack the organelles found in eukaryotic cells, such as the nucleus
or mitochondria.

 Despite their simplicity, prokaryotic cells are highly efficient, with all
life processes occurring within the single cell.

DNA Structure

 In contrast to eukaryotes, prokaryotic cells contain a circular DNA

molecule that is located in the cytoplasm rather than enclosed in a
nuclear envelope.

 This region where DNA is found is referred to as the nucleoid.

 Some prokaryotes also carry additional genetic information in

structures called plasmids.

Reproduction

 Prokaryotic organisms mainly reproduce through a type of asexual

reproduction known as binary fission.

 In this process, the cell’s DNA is copied, and the cell divides into two
identical daughter cells.

Nutrition and Respiration

  Prokaryotes can show different forms of nutrition: some
are photosynthetic, some are chemosynthetic (derive energy from
chemicals), others are heterotrophic.

 While some prokaryotes in certain conditions can carry out aerobic

respiration like eukaryotes, a significant number of prokaryotes
are anaerobes, able to live without dependedance on oxygen.

Distribution and Diversity

 Prokaryotic organisms are found in virtually all environments, from soil

to human skin, to thermal vents on the ocean floor.

 Their capacity for rapid reproduction and genetic variation makes them
very adaptable, contributing immensely to the biodiversity of life on
Earth.

Eukaryotic Organisms
Characteristics of Eukaryotic Organisms

General Properties

 Eukaryotes are one of the key groups of living organisms that fall
under the category of complex forms of life.

 The term Eukaryotic refers to any organism whose cell(s) have a

nucleus and other organelles enclosed within membranes.

 Organisms such as animals, plants, fungi and protists all fall under the
category of eukaryotic organisms.

Cell Complexity

 Eukaryotic cells are typically much larger than prokaryotic cells.

 Eukaryotic cells possess many specialized structures,

termed organelles, that perform specific functions, such as the
nucleus, mitochondria, and chloroplasts.

 In addition to organelles, eukaryotic cells also include a cytoskeleton

for maintaining cell shape and facilitating movement.

DNA Structure

 Unlike prokaryotes, eukaryotic cells keep their genetic material

separated from the rest of the cell by a nuclear envelope, forming a
structure called the nucleus.
 Eukaryotes have linear DNA molecules packed into chromosomes,
which are associated with histone proteins, aiding the organisation of
DNA within the cell.

Reproduction

 Eukaryotic organisms reproduce in many ways, including both asexual

and sexual reproduction.

 Some eukaryotic cells (meiotic cells) undergo meiosis to produce

haploid sex cells or gametes, which can then combine to create new,
genetically unique individuals during sexual reproduction.

Nutrition and Respiration

 Eukaryotic organisms may be photosynthetic (like most

plants), heterotrophic (like animals that ingest nutrients)
or saprotrophic (like fungi that absorb nutrients from dead or
decaying matter).

 Eukaryotes carry out respiration in the mitochondria where they

make use of oxygen to release energy from glucose, this process is
known as aerobic respiration.

Distribution and Diversity

 Eukaryotic organisms are present in nearly all habitats: they are found
in various environments from the deepest oceans to the highest
mountains.

 The kingdom of eukaryotic organisms is extremely diverse and

comprises plants, animals, fungi, and various microorganisms like
protists. Each group has unique characteristics and contributes to
biodiversity on Earth.
Characteristics of Living Organisms
Growth

 All living organisms have the ability to grow.

 This growth is from within, where cells divide and specialise into
different types, leading to increase in size and complexity.

 Organisms not only grow in size, but also in complexity – this is

called development.

Reproduction

 An important property of life is the ability to reproduce or create

organisms like themselves.

 This may be asexual (without the fusion of gametes) or sexual (with

fusion of gametes) reproduction.

 The offspring produced carry characteristics from their parents – this

process is governed by genetics.

Respiration

 All living beings perform a process called respiration, converting food

into usable energy.

 In simple terms, it’s the process of taking in oxygen and giving out
carbon dioxide.

 This energy is used for all activities within the organism.

Sensitivity

 Living organisms are sensitive; they can respond and react to

changes in their environment.

 This response may involve movement, secretion of hormones, or other

physiological changes.
Nutrition

 All organisms take in and use nutrients — substances required for

growth, repair, and normal functioning.

 Autotrophs, such as plants, create their own food, whereas

heterotrophs, such as animals, must ingest their food.

Excretion

 Excretion is the process where waste substances are removed from

the body.

 These waste products are the by-products of metabolic activities, and if

not removed, can be hazardous to the organism.

Movement

 Most living organisms have the ability to move.

 This allows them to respond to their environment in many ways, such

as by finding food, escaping from predators, or seeking a mate.

Remember, the seven characteristics listed above are not just applicable to
animals, but also to plants, fungi, protists, bacteria, and archaea. There is a
huge diversity in the living world, but every organism shares these basic
processes.
Levels of Organization and Cell Structure

Levels of Organisation
Organism, Organ Systems, Organs, Tissues, Cells

 The levels of organisation in biology can be thought of as a

hierarchy, starting from the simplest structures and building up to the
complexity of a whole organism.

Cells

 All living things are made up of cells, which are the smallest unit of
life.

 In animals, these cells include red and white blood cells, nerve cells,
and muscle cells.

 In plants, cell types include root hair cells, xylem, and phloem cells.

Tissues

 A tissue is a group of similar cells that work together to carry out a

particular function.

 Examples of tissues include muscle tissue and nervous tissue in

animals, and epidermis, mesophyll, and vascular tissue in plants.

Organs

 An organ is a group of different types of tissues that work together to

perform a specific function.

 Examples of organs in the human body are the heart, lungs and liver.
In plants, organs include leaves, stems and roots.

Organ Systems
  An organ system is a group of organs that work together to perform a
major function.

 In the human body, examples of organ systems are the circulatory

system, respiratory system, and digestive system. In plants, the root
system and shoot system work together to support growth,
reproduction, and survival.

Organism

 Finally, all of these levels build up to form an organism, a complex

individual living thing.

 Each organism has many organ systems, which contain many organs,
which contain many tissues, which are made up of cells.

An Overview of Biological Organisation

 In summary, the different levels of organisation in biology in order of

increasing complexity are cells, tissues, organs, organ systems, and
organisms.

 Understanding these levels is crucial in the study of biology, as it helps

us understand how the body works, and how different parts interact
and depend on each other.

Biological Molecules
Carbohydrates

 Carbohydrates are energy-providing nutrients composed of carbon,

hydrogen, and oxygen.

 They can be classified into three main types: monosaccharides,

disaccharides, and polysaccharides.

 Monosaccharides are the simplest form of carbohydrate like glucose

and fructose.

 Two monosaccharides join to form a disaccharide such as sucrose.

 Hundreds or thousands of monosaccharides can combine to

form polysaccharides such as starch and cellulose.
Lipids

 Lipids are known as fats and oils, composed of carbon, hydrogen, and
a small amount of oxygen.

 They function as a long-term energy store, insulators against heat loss

and a protective layer around delicate organs.

 Lipids are classified into two types: saturated and unsaturated lipids.

 Saturated lipids contain only single bonds between carbon atoms,

while unsaturated lipids contain at least one carbon-carbon double
bond.

Proteins

 Proteins are large complex molecules made up of amino acids,

composed of carbon, hydrogen, oxygen, and nitrogen.

 They play a vital role in structural support, transport, enzymes,

antibodies and hormones.

 The shape and function of a protein is determined by its specific

arrangement of amino acids, which is coded by DNA.

Nucleic Acids

 Nucleic acids are composed of nucleotides, which are made up of a

sugar, a phosphate group, and a nitrogenous base.

 Two main types of nucleic acids include DNA and RNA.

 DNA or deoxyribonucleic acid contains all the instructions needed to

build and maintain an organism.

 RNA or ribonucleic acid translates the genetic information within DNA

into proteins needed by the cell.

Enzymes

 Enzymes are biological catalysts that speed up biochemical reactions

in the cell.

 They can do so without being consumed within the process.

 The specific shape of an enzyme’s active site matches the shape of its
substrate—the molecule it acts upon.
 Each enzyme is specific as it will only catalyse one particular reaction.
Each enzyme works best at its optimum temperature and pH.

Movement of Substances into and out of

Cells
Diffusion

 Diffusion is a method of transporting materials in and out of cells and

it is driven by a concentration gradient.

 It is a passive process, which means it does not require energy from

the cell.

 It involves the movement of particles from an area of higher

concentration to an area of lower concentration until they are evenly
distributed.

 Oxygen and carbon dioxide are often transported by diffusion.

Osmosis

 Osmosis is a special type of diffusion involving the movement of water

molecules across a selectively permeable membrane.

 Like diffusion, it is a passive process and doesn’t require energy,

instead it relies on differences in water concentration.

 Water moves from a region of higher water concentration (lower solute

concentration) to a region of lower water concentration (higher solute
concentration) through the cell membrane.

 Osmosis is critical for the absorption of water in plant roots and the
absorption and release of water in all cells.

Active Transport
 In contrast to diffusion and osmosis, active transport does require
energy to move substances across cell membranes.

 This energy is usually sourced from ATP, the cell’s energy storage
molecule.

 Active transport mechanisms move substances from an area of lower

concentration to an area of higher concentration, working against the
concentration gradient.

 Active transport is necessary when the cell needs substances that are
not in abundance in the environment, such as glucose or ions.

Factors Affecting the Rate of Transport

 The rate of substance transport into and out of cells is influenced

by a number of factors: temperature, surface area, length of diffusion
paths and concentration gradients.

 Higher temperatures increase the rate because the particles have

more energy and move more quickly.

 Greater surface area of the cell membrane also increases the rate as
there is more area for substances to move across.

 Shorter diffusion paths increase the rate because the substances have
less distance to travel.

 A steeper concentration gradient increases the rate because the

difference between concentrations inside and outside the cell is
greater, driving faster movement.

Nutrition
Introduction

 Nutrition is the process where organisms take in nutrients to provide

energy, promote growth, and maintain bodily functions.

 Nutrients
include carbohydrates, proteins, lipids, vitamins, minerals, wate
r and fibre.

Human Nutrition

 Humans are omnivores meaning that they consume both plants and
animals.
 Humans require a balanced diet which contains the right amounts and
types from each food group – carbohydrates, proteins, lipids, fruits,
vegetables, around 8 cups of water daily, and no more than 6g of salt.

 Digestion in humans begins in the mouth, where food is broken down

mechanically by teeth and chemically by saliva.

 The main site of digestion and absorption is the small intestine where
nutrients are absorbed into the bloodstream through finger-like
projections called villi.

 Water and left-over nutrients are absorbed in the large intestine,

forming feces which are egested through the rectum.

Plant Nutrition

 Plants are autotrophs, meaning they produce their own food through
photosynthesis.

 For photosynthesis, plants require light, carbon dioxide, and water. The
process produces glucose and oxygen.

 In addition to these requirements, plants also require mineral ions such

as nitrates for protein synthesis.

 Some plants, known as insectivorous plants, such as the Venus flytrap,

also get their nutrients from trapping and digesting small insects.

Animal Nutrition

 Animals are heterotrophs, meaning they ingest other organisms or

organic matter to obtain their nutrients.

 Herbivores eat plant material, carnivores eat other animals, and

omnivores eat a combination of both.

 In animals, digestion involves both mechanical and chemical

breakdown of food. This process varies widely depending on the diet
and feeding habits of the animal.

 Ruminant animals like cows have a unique digestive system, including

a four-chambered stomach, to allow them to effectively digest grass
and other plant material.

Respiration
 Overview of Respiration

 Respiration is the process by which living organisms take in oxygen

and release carbon dioxide.

 It is a series of complex chemical reactions that occur in every living

cell, providing the energy needed for life processes.

 This energy is mostly used for growth, repair, active transport,

maintaining body temperature, and the synthesis of larger molecules.

Aerobic Respiration

 Aerobic respiration requires oxygen and is the most efficient form of

respiration.

 The overall equation for aerobic respiration in glucose is:

o C6H12O6 (Glucose) + 6O2 (Oxygen) → 6CO2 (Carbon

Dioxide) + 6H2O (Water) + Energy

 The breakdown of glucose occurs in four stages: Glycolysis, the Link

Reaction, the Krebs Cycle, and the Electron Transport Chain.

 This process happens in the mitochondria of the cells.

Anaerobic Respiration

 Anaerobic respiration does not require oxygen. It is a less efficient

process than aerobic respiration because it releases less energy
overall.

 In humans, anaerobic respiration results in lactic acid:

o Glucose → Lactic Acid + Energy

 In yeast cells, anaerobic respiration results in ethanol and carbon

dioxide, a process commonly known as fermentation.

o Glucose → Ethanol + Carbon Dioxide + Energy

 Since less energy is produced, anaerobic respiration can only be

sustained for a short period of time.

Comparison of Aerobic and Anaerobic Respiration

 While both processes provide energy, aerobic respiration releases

more energy because it fully breaks down glucose into carbon dioxide
and water.
 Anaerobic respiration occurs when there is insufficient oxygen for
aerobic respiration, like in intensive exercise or in low oxygen
conditions.

 Anaerobic respiration can result in muscle fatigue when lactic acid

builds up in the muscle cells.

Understanding Respiration

 While it is referred to as ‘breathing’, respiration is not the inhalation

and exhalation of air but rather the use of oxygen to release energy
from glucose.

 It is an essential process for life, contributing to various functions in the

body including growth, muscle movement, and maintaining body
temperature. It is key to understand the role of respiration in the larger
biological systems.

Gas Exchange
 Gas exchange is the process where oxygen (O2) and carbon dioxide
(CO2) move between organisms and their environment.

 This process involves diffusion of gases where they move from an area
of higher concentration to an area of lower concentration.

 Gas exchange takes place at a respiratory surface — a boundary where

oxygen in the air or water meets the body’s circulating blood.

In Humans

 In humans, the main respiratory surface is the alveoli in the lungs.

 When we breathe in, oxygen in the air fills the alveoli.

 Oxygen then diffuses across the alveolar walls into the surrounding
capillaries, where it binds to haemoglobin in red blood cells.

 At the same time, carbon dioxide in deoxygenated blood diffuses into

the alveoli to be breathed out.

In Plants

 In plants, gas exchange happens in tiny pores in leaves

called stomata.
 Carbon dioxide from the air diffuses through the stomata into the plant
during photosynthesis.

 Oxygen produced during photosynthesis diffuses out of the plant

through the stomata.

 At night, when photosynthesis isn’t happening, oxygen is used by the

plant in respiration, and excess carbon dioxide diffuses out through the
stomata.

In Fish

 In fish, gas exchange occurs in their gills.

 Oxygen dissolved in water diffuses into gill capillaries, while carbon

dioxide in the blood diffuses out into the water.

Factors Affecting Gas Exchange

 Temperature: Higher temperatures increase the rate of gas exchange

as the gases have more energy and move more quickly.

 Surface area: An increased surface area of the respiratory organ

allows for more gas exchange to occur simultaneously.

 Concentration gradient: A large difference in the concentration of

gases inside and outside the respiratory organ can cause gases to
diffuse more quickly.

 Moisture: Many respiratory surfaces need to be moist for gases to

dissolve and diffuse across them.

Transport
Transport in Cells

 Transport in cells refers to the movement of materials into, out of, and
within cells. This includes the movement of water, ions, and other
substances like glucose and amino acids.

 Transport can be either passive (not requiring energy)

or active (requiring energy).

Diffusion
 Diffusion is a passive form of transport, moving substances from a
region of high concentration to an area of low concentration until a
balance is achieved, also known as equilibrium.

 The rate of diffusion depends on temperature, concentration gradient,

and the surface area to volume ratio of the diffusing substance.

Osmosis

 Osmosis is a specific kind of diffusion and involves the movement of

water molecules.

 In osmosis, water moves from an area of high water potential (or low
solute concentration) to an area of low water potential (or high solute
concentration).

 The rate of osmosis is affected by the concentration gradient,

temperature and surface area to volume ratio.

Active Transport

 Active transport is the transfer of ions or molecules across a cell

membrane from an area of lower concentration to an area of higher
concentration.

 It requires energy in the form of ATP because it is moving substances

against the concentration gradient.

 Active transport enables cells to absorb ions from very dilute solutions,
an essential mechanism in plants for obtaining nutrients from the soil.

Transport in the Human Body

 The human body uses a circulatory system for transportation of

substances.

 Blood transports nutrients, oxygen, carbon dioxide, hormones, and

heat around the body.

 The heart pumps the blood, and the blood vessels (arteries, veins,
and capillaries) serve as the transport routes.

 Arteries carry blood away from the heart, veins bring blood back to the
heart, and capillaries connect arteries and veins.

Transport in Plants

 In plants, the xylem and phloem play crucial roles in transport.

 Xylem moves water and dissolved minerals from the roots to other
parts of the plant.

 Phloem transports sugars, amino acids, and other organic products

from leaves (where photosynthesis takes place) to other parts of the
plant.

Hope this helps you in revising the topic of “Transport” for your
Structure and Functions in Living Organisms module!