These notes are highlighted from our A-level Biology exam focus textbook, for complete study materials on this course, refer to the textbook. For effective preparation, practice past questions on this course as much as possible.
Topic 8: Basic Characteristics and Diversity of Plants
Plants are living organisms that are broadly divided into two major groups which are lower plants and higher plants. Lower plants are simpler and less complex in their structure while higher plants are more advanced and complex.
Lower plants are further divided into smaller groups. Algae are simple aquatic plants and common examples include Chlorella, Chlamydomonas, Volvox, and Spirogyra. Fungi are organisms that feed on dead or living organic matter and examples include yeast, Rhizopus, Mucor, Aspergillus, Penicillium, mushroom, and Phytophthora. Bryophytes are small land plants that need moisture to survive and examples include Riccia, Marchantia, and Funaria. Pteridophytes are slightly more complex plants that have simple vascular tissue and examples include Lycopodium, Selaginella, and Nephrolepis.
Higher plants are divided into non-vascular and vascular plants. Spermatophytes are seed-bearing vascular plants and examples include Cycas, Pinus, Gnetum, and Hibiscus rosa-sinensis. Each group of plants has its own morphology, life cycle, and ecological or economic importance that students are expected to study and understand.
Topic 9: Taxonomy of Lower and Higher Plants
Plant taxonomy is the science of naming and classifying plants into groups based on their features and relationships. Plant nomenclature refers to the system of giving plants their scientific names, following the same binomial nomenclature system used for all living things.
Plant classification arranges plants from the broadest group down to the most specific, moving through kingdom, division, class, order, family, genus, and species. It is important to understand the difference between taxonomy and systematics. Taxonomy focuses on naming and classifying plants while systematics is broader and also looks at the evolutionary relationships between plant groups.
Topic 10: Plant Conservation
Plant conservation is the effort to protect plant species and their habitats from destruction and extinction. There are two main approaches to conservation.
In-situ conservation means protecting plants within their natural habitat. An example is a forest reserve or a national park. The advantage is that plants continue to grow naturally in their environment. The disadvantage is that natural habitats can still be destroyed by human activities or climate change.
Ex-situ conservation means protecting plants outside their natural habitat. Examples include botanical gardens and seed banks. The advantage is that plants are protected from environmental threats. The disadvantage is that they are removed from their natural ecological setting and may not thrive as well.
Biological control is another aspect of conservation where natural predators or organisms are used to manage pests instead of chemical pesticides, which can harm plants and the environment. Climate change poses a serious threat to plants because rising temperatures, unpredictable rainfall, and extreme weather events disturb the conditions that many plant species need to survive.
Topic 11: Plant Tissues and Functions
A tissue is a group of similar cells that work together to perform a specific function. Plants have several types of tissues, each with its own composition and role.
Parenchyma tissue is the most common plant tissue. It is made up of loosely packed living cells and is involved in photosynthesis, storage, and basic metabolic activities. Collenchyma tissue provides flexible support to growing parts of the plant such as young stems and leaf stalks. Its cells have thickened walls but remain living. Sclerenchyma tissue provides rigid support and protection. Its cells have very thick walls and are usually dead at maturity.
Epidermal tissue forms the outer covering of plant organs like leaves, stems, and roots. It protects the plant from water loss and physical damage. Peridermal tissue replaces the epidermis in older stems and roots as the plant grows thicker. It forms what we commonly see as bark on woody plants.
Vascular tissue is responsible for transporting substances throughout the plant. It consists of xylem, which transports water and dissolved minerals from the roots upward to the rest of the plant, phloem, which transports food produced by photosynthesis from the leaves to other parts of the plant, and cambium, which is a layer of dividing cells that produces new xylem and phloem as the plant grows.
In practical class students observe osmosis and transpiration in plants to understand how water moves through plant tissues.
Topic 12: Plant Morphology and Anatomy
Morphology refers to the external structure and form of a plant while anatomy refers to the internal arrangement of tissues. Both are important for understanding how plants function and adapt to their environment.
Roots anchor the plant in the soil and absorb water and minerals. There are two main root systems. The taproot system has one main root that grows deep into the soil with smaller branches coming off it. The fibrous root system has many roots of similar size spreading out from the base of the stem. Roots can also be modified for special functions such as storage in carrots or support in maize.
Stems support the plant and serve as pathways for transporting water and food between roots and leaves. Stems can also be modified for storage, climbing, or reproduction. The anatomy of monocot stems differs from dicot stems mainly in how the vascular bundles are arranged. In monocots the bundles are scattered throughout the stem while in dicots they are arranged in a ring.
Leaves are the main organs of photosynthesis. They can be simple, meaning they have one blade, or compound, meaning the blade is divided into smaller leaflets. Leaves are also arranged differently on stems and can be modified for purposes like storing water, catching insects, or climbing. The internal anatomy of a leaf includes the epidermis on the outside, the mesophyll where photosynthesis takes place, and the vascular bundles that supply water and remove food.
Flowers are the reproductive organs of flowering plants. A typical dicot flower has sepals, petals, stamens which are the male parts, and a pistil which is the female part. Floral diagrams and formulae are used to represent the structure of flowers in a simplified way.
Fruits develop from the ovary of a flower after fertilization. They can be dry and dehiscent, meaning they split open to release seeds, dry and indehiscent, meaning they do not split open, or fleshy fruits that are soft and contain seeds inside. Students are expected to draw longitudinal and transverse sections of different fruit types.
Topic 13: Nutrition in Plants
Plants make their own food through a process called photosynthesis, which makes them autotrophs. There are two types of autotrophic nutrition. Photosynthetic plants use sunlight as their energy source while chemosynthetic organisms use chemical energy.
Photosynthesis takes place in two stages. The light reaction occurs in the presence of sunlight and takes place in the thylakoid membranes of the chloroplast. During this stage light energy is used to split water molecules and produce ATP and NADPH. The dark reaction, also called the Calvin cycle, does not require direct light and takes place in the stroma of the chloroplast. During this stage carbon dioxide is used to produce glucose using the energy from the light reaction.
Some plants are heterotrophic, meaning they cannot make their own food and depend on other organisms. Holozoic nutrition involves ingesting solid food, which is seen in some insectivorous plants.
Plants also require mineral elements for healthy growth. Nitrogen is needed for protein synthesis. Phosphorus supports root development and energy transfer. Potassium helps with water regulation and enzyme activation. When these minerals are lacking, plants show visible deficiency symptoms such as yellowing of leaves, stunted growth, or poor fruit development. Chemical fertilizers are used to supply these minerals to plants in agriculture.
In practical class students observe etiolation which is the pale and weak growth that occurs when plants grow without enough light, measure photosynthesis in leaves, conduct growth experiments to observe deficiency symptoms, and go on field studies to identify deficiency symptoms in real plants.
Topic 14: Transport System in Plants
Plants need to move water, minerals, and food to different parts of the body and this is done through two types of vascular tissue.
Xylem transports water and dissolved mineral salts from the roots up to the leaves and other parts. This movement is driven mainly by transpiration, which is the loss of water vapor through tiny pores in the leaves called stomata. As water evaporates from the leaves it creates a pulling force that draws water upward through the xylem.
Phloem transports food, mainly in the form of sucrose, from the leaves where it is produced to other parts of the plant that need it. This movement is called translocation and it can go both upward and downward depending on where the food is needed.
Osmosis is also important in plant transport. It is the movement of water from an area of low solute concentration to an area of high solute concentration through a semi-permeable membrane. This process helps roots absorb water from the soil.
In practical class students observe and demonstrate transpiration, osmosis, and food transport in plants.
Topic 15: Respiration in Plants
Plants also respire just like animals do. Respiration is the process by which living cells break down food to release energy for use in biological activities.
Plants exchange gases through special structures. Stomata are tiny pores found mainly on the surface of leaves. Each stoma is surrounded by two guard cells that control its opening and closing. When stomata open, carbon dioxide enters for photosynthesis and oxygen and water vapor are released. Lenticels are small pores found on the surface of woody stems and roots that allow gas exchange when stomata are not available.
There are two types of respiration. Aerobic respiration occurs in the presence of oxygen and produces carbon dioxide, water, and a large amount of energy. This is the most common and efficient type. Anaerobic respiration occurs without oxygen and produces alcohol and carbon dioxide along with a much smaller amount of energy. This type occurs in conditions where oxygen is limited such as in waterlogged soils.
Topic 16: Plant Reproduction
Flowering plants, also called angiosperms, reproduce through flowers. There are differences between monocot and dicot flowers. Monocot flowers have flower parts in multiples of three while dicot flowers have parts in multiples of four or five. Monocots also have one seed leaf while dicots have two.
Pollination is the transfer of pollen from the anther to the stigma of a flower. It can happen through wind, water, insects, birds, or other agents. After pollination, fertilization occurs when the pollen travels down to the ovule and fuses with the egg cell. This produces a seed that develops inside a fruit.
Plants can also reproduce asexually through methods like budding, runners, bulbs, corms, and rhizomes.
Topic 17: Growth Regulators
Plants produce chemical substances called growth regulators or plant hormones that control and coordinate their growth and development.
Auxins are produced at the tips of shoots and roots and they promote cell elongation. They cause plants to bend toward light in a process called phototropism. Gibberellins promote stem elongation, seed germination, and fruit development. Cytokinins promote cell division and help delay the aging of plant tissues. Ascorbic acid, which is vitamin C, acts as an antioxidant and plays a role in cell growth and repair. Ethylene is a gas that promotes the ripening of fruits and also plays a role in leaf fall.
Topic 18: Crop Improvement
Crop improvement involves using scientific methods to develop better varieties of crops that produce more yield, resist diseases, or adapt to difficult environmental conditions.
Genetically Modified Crops are crops whose genetic material has been altered in a laboratory to give them desirable traits such as pest resistance, drought tolerance, or improved nutritional content. However, the development of resistant plant species is a challenge because pests and diseases can also evolve and overcome the resistance built into crops.
Genetic modification also comes with ethical implications. Some people are concerned about the safety of genetically modified foods, their impact on natural ecosystems, and the control that large companies have over the food supply through patented seeds.
Topic 19: Economic and Ecological Importance of Plants
Plants are extremely important to both human life and the environment. Economically important food plants include rice, maize, wheat, cassava, and yam which form the basis of diets around the world. Economically valuable medicinal plants include those used to produce drugs, herbal remedies, and traditional medicines that treat various illnesses.
Ornamental plants are grown for their beauty and are used in landscaping, decoration, and gardening. Beyond their economic value, plants play a crucial ecological role by producing oxygen, absorbing carbon dioxide, preventing soil erosion, providing habitat for animals, and maintaining the balance of ecosystems.