Plant Growth: Primary & Secondary

Primary Growth

• Primary growth in plants mainly leads to an increase in length.
• Apical meristem is responsible for primary growth.
• Primary growth occurs in root and stem tips.
• Epidermis, cortex, and primary xylem/phloem tissues form during primary growth.
• The plant hormone auxin mainly promotes primary growth.

Secondary Growth

• Secondary growth in plants mainly leads to an increase in thickness/girth.
• Lateral meristems facilitate secondary growth.
• Vascular cambium is a lateral meristem.
• Vascular cambium gives rise to secondary xylem and phloem.
• Phellogen is also known as cork cambium.
• Periderm is the outer protective layer formed during secondary growth.
• Stems of monocots do not typically undergo secondary growth.
• Seasonal activity of vascular cambium causes annual rings in wood.
• Bark includes all tissues outside vascular cambium.
• The epidermis is not part of the secondary plant body.

Simple Permanent Tissues

• Xylem is not a simple permanent tissue.
• Parenchyma cells are usually thin-walled and living.
• Collenchyma provides mechanical support and elasticity to plants.
• Mechanical support is the main function of sclerenchyma.
• Sclerenchyma is a simple tissue with cells that have uniformly thickened walls and are usually dead at maturity.

Complex Permanent Tissues

• Xylem is a complex permanent tissue.
• Phloem transports food.
• Sieve tubes are not part of xylem.
• Companion cells are associated with sieve tube elements.
• Tracheids are dead xylem elements that aid in water conduction.

Pholem

• Sieve tubes, a component of pholem, are living but lack a nucleus.
• Phloem fibers are unique because they are dead.

Xylem

• Vessels are the most efficient conducting cells of xylem in angiosperms.

Respiration

• Mitochondria is the main site of aerobic respiration in plant cells.
• The process of breaking down glucose to release energy is respiration.
• Oxygen is not a product of aerobic respiration in plants.
• Respiration occurs in all living parts of a plant.
• Ethanol and carbon dioxide are the end products of anaerobic respiration in plants.
• Energy is released as ATP during respiration.
• Glycolysis, the first step of respiration, occurs in the cytoplasm.
• Oxygen is absorbed during respiration in plants.

Plant Tissue Culture

• Agar is used as a gelling agent in plant tissue culture media.
• Murashige and Skoog first developed the nutrient medium for plant tissue culture.
• Auxin promotes root formation in tissue culture.
• Totipotency is the ability of a cell to regenerate into a whole plant.
• Glucose is not a sterilizing agent used in plant tissue culture.
• Callus is an undifferentiated mass of cells.
• The explant is a small piece of tissue used to initiate culture.
• Sucrose is most commonly used as a carbon source in plant tissue culture media.
• Somatic embryogenesis is the formation of embryos from somatic cells.
• Rapid multiplication of disease-free plants is the primary use of micropropagation.
• An explant is the most commonly used part to initiate plant tissue culture.
• Soil is not a requirement for plant tissue culture.
• Auxins mainly promote root formation in plant tissue culture.

Roots

• Roots anchor the plant and absorb water.
• Xylem transports water from roots to other parts of the plant.
• Photosynthesis is not a function of roots.
• The root hair zone is responsible for water absorption.
• The epidermis is the outermost layer of a root.
• Fibrous root systems are commonly found in monocots.
• The root cap is the protective structure at the tip of the root.
• The meristematic region is where cells continuously divide in the root.

Stem

• Stems do not absorb nutrients from soil.
• Photosynthesis is not a function of the stem.
• Rhizomes are stem modifications used for food storage.
• The epidermis is the outer protective layer of the stem.

Leaves

• Leaves are responsible for photosynthesis.
• Palisade mesophyll is the part of the leaf where photosynthesis occurs.
• Stomata in leaves function to exchange gases.
• A cuticle is a waxy layer prevents water loss on the leaf.
• Guard cells control stomata opening and closing.
• Xylem transports water to the leaf.
• The lower epidermis of a leaf contains more stomata.
• Spongy mesophyll contains loosely packed cells with air spaces to facilitate gas exchange.

Other Components

• Fruits contains seeds.

Secondary Metabolites

• Proteins are not a class of plant secondary metabolites.
• Alkaloid is the class of secondary metabolite that morphine belongs to.
• Quinine is a secondary metabolite used as an anti-malarial drug.
• Terpenoids are responsible for the aroma in plants like mint.
• Photosynthesis is not a function of secondary metabolites in plants.

Nutrients

• Magnesium is essential for chlorophyll synthesis in plants.
• Phosphorus is primarily responsible for root development.
• Nitrogen enhances chlorophyll production and vegetative growth.
• Opening and closing of stomata requires potassium.
• Potassium is involved in the activation of enzymes and carbohydrate metabolism.
• Calcium is essential for membrane stability and cell wall structure in plants.
• Molybdenum is required for nitrogen fixation in legumes.
• Iron is primarily involved in chlorophyll synthesis.
• A high cytokinin to low auxin hormone combination favors shoot formation in vitro.
• Subculturing in plant tissue culture helps multiply the callus or shoots.
• A specific balance of plant growth regulators induces somatic embryogenesis.
• Nitrogen is a primary macronutrient for plants.

Macro/Micronutrients

• Magnesium is essential for chlorophyll synthesis.
• Plants require micronutrients in trace amounts.
• Potassium (K) is not a micronutrient.
• Phosphorus is important for root development.
• Calcium is classified as a secondary macronutrient.
• Chlorosis (yellowing) of young leaves is caused by iron deficiency.

Biotechnology

• Plant biotechnology is the application of technology to modify plants for specific purposes, for increased yield, disease resistance, or nutritional value.
• The explant is used in plant tissue culture.
• Tomato was the first genetically modified crop.
• A protoplast is a plant cell without a cell wall.
• Marker genes in genetically modified plants are used to identify transformed cells.