Characteristics of Living Organisms
Living organisms share several essential characteristics:
Nutrition: They require nutrients for energy and growth.
Respiration: They convert nutrients into energy.
Excretion: They eliminate waste products from their bodies.
Response to Surroundings: They respond to stimuli in their environment.
Movement: They can move or change position.
Internal Control: They regulate internal conditions (homeostasis).
Reproduction: They can reproduce to create new organisms.
Growth and Development: They grow and develop over time.
Variety of living organisms:
Eukaryotic Organisms
1. Plants:
○ Multicellular with chloroplasts for photosynthesis.
○ Cell walls made of cellulose.
○ Store carbohydrates as starch or sucrose.
○ Examples: Maize (cereal), peas, beans.
2. Animals:
○ Multicellular without chloroplasts; cannot photosynthesize.
○ No cell walls; typically have nervous coordination.
○ Store carbohydrates as glycogen.
○ Examples: Humans (mammals), houseflies, mosquitoes (insects).
3. Fungi:
○ Non-photosynthetic; composed of mycelium made of hyphae.
○ Cell walls made of chitin; often store carbohydrates as glycogen.
○ Feed through saprotrophic nutrition (extracellular digestion).
○ Examples: Mucor (fungal hyphae), yeast (single-celled).
4. Protoctists:
○ Microscopic, mostly single-celled organisms.
○ Some resemble animal cells (e.g., Amoeba), while others have
chloroplasts (e.g., Chlorella).
○ Includes pathogens like Plasmodium, which causes malaria.
Pathogens
Pathogens are organisms that can cause disease and include:
● Fungi
● Bacteria
● Protoctists
● Viruses: Non-living entities that reproduce only inside living cells, with a
protein coat and either DNA or RNA. Examples include the tobacco mosaic
virus, influenza virus, and HIV.
Structure of functions in living organisms:
Levels of Organization
1. Organelles: The specialized structures within a cell (e.g., nucleus,
mitochondria).
2. Cells: The basic unit of life.
3. Tissues: Groups of similar cells working together (e.g., muscle tissue).
4. Organs: Structures made of different tissues performing specific functions
(e.g., heart).
5. Systems: Groups of organs working together (e.g., circulatory system).
Cell Structure
Nucleus: Contains genetic material; controls cell activities.
Cytoplasm: Jelly-like substance where cellular processes occur.
Cell Membrane: A semi-permeable barrier controlling entry and exit of
substances.
Cell Wall: Rigid outer layer in plant cells for support (made of cellulose).
Mitochondria: Powerhouses of the cell; site of respiration and energy production.
Chloroplasts: Organelles in plant cells for photosynthesis (contain chlorophyll).
Ribosomes: Sites of protein synthesis.
Vacuole: Storage space; larger in plant cells for maintaining turgor pressure.
Similarities and Differences
● Plant Cells: Have cell walls, chloroplasts, and large vacuoles.
● Animal Cells: Lack cell walls and chloroplasts; have smaller vacuoles.
Biological Molecules
Chemical Elements:
● Carbohydrates: Composed of carbon, hydrogen, and oxygen.
● Proteins: Made of amino acids (contain carbon, hydrogen, oxygen, and
nitrogen).
● Lipids: Composed of fatty acids and glycerol (contain carbon, hydrogen, and
oxygen).
Structure:
● Carbohydrates: Large molecules like starch and glycogen derived from
simple sugars.
● Proteins: Formed from chains of amino acids.
● Lipids: Composed of fatty acids and glycerol.
Enzymes: Biological catalysts that speed up metabolic reactions; affected by
temperature and pH.
Nutrition
Flowering Plants
1. Photosynthesis: Process of converting light energy to chemical
energy (glucose).
○ Word Equation: Carbon dioxide + Water → Glucose +
Oxygen.
○ Balanced Equation: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂.
○ Factors affecting rate: Light intensity, carbon dioxide
concentration, temperature.
2. Leaf Structure: Adapted for efficient photosynthesis, with
chloroplasts and a large surface area.
3. Mineral Ions: Essential for growth (e.g., magnesium for
chlorophyll, nitrate for amino acids).
Humans
1. Balanced Diet: Includes carbohydrates, proteins, lipids, vitamins,
minerals, water, and dietary fiber.
2. Alimentary Canal: Structure includes mouth, esophagus, stomach,
small intestine, large intestine, and pancreas.
3. Digestive Enzymes: Break down macromolecules into smaller units
(e.g., starch to glucose, proteins to amino acids).
Respiration
1. ATP Production: Respiration produces ATP, providing energy for cellular
processes.
2. Types of Respiration:
○ Aerobic: Requires oxygen; produces more ATP.
○ Anaerobic: Occurs without oxygen; produces less ATP.
○ Equations:
■ Aerobic: Glucose + Oxygen → Carbon Dioxide + Water +
Energy.
■ Anaerobic (in animals): Glucose → Lactic Acid + Energy.
3. Gas Exchange: Involves the structure of the thorax, including alveoli
adapted for efficient gas exchange.
Circulatory System
1. Blood Composition: Composed of red blood cells, white blood cells,
platelets, and plasma.
2. Heart Structure: Pumps blood through the body; heart rate
changes with exercise and adrenaline.
3. Blood Vessels: Arteries (carry blood away from heart), veins (carry
blood to heart), capillaries (exchange substances).
Excretion
1. Excretory Products: Includes carbon dioxide (lungs), urea
(kidneys), and sweat (skin).
2. Stomata: Sites for gas exchange in plants, allowing oxygen and
carbon dioxide loss.
Reproduction and Inheritance:
Reproduction
● Sexual Reproduction:
○ Involves the fusion of male and female gametes.
○ Produces genetically diverse offspring (zygote).
○ Requires fertilization.
● Asexual Reproduction:
○ Involves a single parent.
○ Offspring are genetically identical to the parent (clones).
○ Does not require fertilization.
3.2 Fertilization Process
● Fertilization is the fusion of a male gamete (sperm) and a female gamete (egg)
to form a zygote.
● The zygote undergoes cell division and develops into an embryo.
Flowering Plants
3.3 Structures of Pollinated Flowers
● Insect-Pollinated Flowers:
○ Brightly colored petals to attract insects.
○ Scented and produce nectar.
○ Stigma is sticky to catch pollen.
● Wind-Pollinated Flowers:
○ Small, inconspicuous petals.
○ Produces large amounts of lightweight pollen.
○ Stigma is feathery to catch airborne pollen.
3.4 Pollen Tube Growth and Fertilization
● After pollination, the pollen tube grows down the style to the ovule.
● Fertilization occurs when the sperm travels down the pollen tube to fuse with
the egg, forming seed and fruit.
3.5 Conditions for Seed Germination
● Investigate the necessary conditions for seed germination, including moisture,
temperature, and oxygen availability.
3.6 Utilization of Food Reserves
● Germinating seeds use stored food reserves (starch, proteins) until the
seedling can photosynthesize.
3.7 Asexual Reproduction in Plants
● Natural Methods:
○ Runners (e.g., strawberries) propagate new plants.
● Artificial Methods:
○ Cuttings can be taken from a parent plant to produce new plants.
Humans
3.8 Structure of Reproductive Systems
● The male and female reproductive systems are adapted for their specific
functions:
○ Male: Produces and delivers sperm.
○ Female: Produces eggs and supports embryo development.
3.9 Roles of Hormones in the Menstrual Cycle
● Oestrogen: Regulates the menstrual cycle and promotes the growth of the
uterine lining.
● Progesterone: Maintains the uterine lining for potential implantation of an
embryo.
3.11 Role of the Placenta
● The placenta facilitates the exchange of nutrients, gases, and waste between
the mother and developing embryo.
3.12 Protection of the Developing Embryo
● The developing embryo is protected by amniotic fluid within the amniotic sac,
providing cushioning and a stable environment.
3.13 Hormones and Secondary Sexual Characteristics
● Oestrogen: Promotes the development of female secondary sexual
characteristics.
● Testosterone: Promotes the development of male secondary sexual
characteristics.
Inheritance:
Genome and Genes
● Genome: The complete set of DNA in an organism, including all of its genes.
● Gene: A specific segment of DNA that contains the instructions for
synthesizing a particular protein. Genes are the units of heredity.
Alleles
● Alleles: Different versions of a gene that exist at the same locus on
homologous chromosomes. Alleles can result in variations in inherited traits
(e.g., flower color, eye color).
Genetic Terminology
1. Dominant: An allele that expresses its trait even in the presence of a
different allele. It masks the effect of a recessive allele.
○ Example: In a heterozygous genotype (Aa), the dominant allele (A)
determines the phenotype.
2. Recessive: An allele that only expresses its trait when two copies are present
(homozygous condition). It is masked by a dominant allele.
○ Example: The recessive allele (a) is only expressed in the homozygous
condition (aa).
3. Homozygous: Having two identical alleles for a particular gene (e.g., AA or
aa). This can be either dominant or recessive.
4. Heterozygous: Having two alleles for a particular gene (e.g., Aa). This
results in the expression of the dominant trait.
5. Phenotype: The observable physical or biochemical characteristics of an
organism, determined by both genetic makeup (genotype) and environmental
factors.
○ Example: A plant's flower color, height, or leaf shape.
6. Genotype: The genetic constitution of an organism; the specific alleles
present (e.g., AA, Aa, or aa).
Shortcut:
MRS H GREN
M: Movement - Living organisms can move, whether it is the movement of the whole
organism or the movement of substances within it.
R: Respiration - Organisms carry out respiration to convert food into energy.
S: Sensitivity - Living things can respond to stimuli in their environment.
H: Homeostasis - Organisms regulate their internal environment to maintain stable
conditions (e.g., temperature, pH).
G: Growth - Living organisms grow and develop throughout their life cycle.
R: Reproduction - All living organisms have the ability to reproduce, either sexually or
asexually.
E: Excretion - Organisms can eliminate waste products produced during metabolic
processes.
N: Nutrition - Living organisms require nutrients for energy, growth, and repair.
CORMS
C: Cells - All living organisms are made up of cells, which are the basic units of life.
O: Organization - Living organisms exhibit a complex organization, from cellular
structures to tissues, organs, and systems.
R: Response to stimuli - Organisms can respond to changes in their environment, which
is essential for survival.
M: Metabolism - All living things carry out metabolic processes, including chemical
reactions that convert energy and matter.
S: Stability (or Homeostasis) - Living organisms maintain stable internal conditions
despite external changes.
