Chapter 1: Organisation of Plant Tissues and Growth

1.1 Organisation of Plant Tissues

• A plant consists of meristematic tissues and permanent tissues. (p.4)
• Meristematic tissues are actively dividing tissues through mitosis. (p.4)
• Permanent tissues are matured tissues that have undergone or are undergoing differentiation: epidermal, ground and vascular tissues. (p.4)
• Epidermal tissues cover the outer surface of stems, leaves and young roots. (p.5)
• The cuticle is a waxy, waterproof layer on exposed epidermal cell walls; it reduces transpiration and protects against mechanical injury and pathogens. (p.5)
• Guard cells control the opening of the stoma; root hair cells increase the surface area for absorbing water and mineral salts. (p.5)
• Parenchyma tissues are the simplest living cells with the thinnest cell walls; they store starch and sugar, carry out photosynthesis and gaseous exchange, and help repair tissues. (p.5)
• Collenchyma tissues are living cells with pectin and hemicellulose walls that are thicker than parenchyma; they give flexibility and mechanical support. (p.5)
• Sclerenchyma tissues consist of dead mature cells with the thickest walls among the ground tissues; they provide strength and support. (p.5)
• Xylem consists of dead cells without cytoplasm; its walls contain lignin; it transports water and mineral salts from roots to all parts. (p.5)
• Phloem consists of living sieve tubes and companion cells; it transports sugars from leaves to storage organs such as roots, fruits and tubers. (p.5)

1.2 Meristematic Tissues and Growth

• Apical meristems are located at the tips of shoots and roots; lateral meristems consist of vascular cambium and cork cambium. (p.6)
• Growth is the change from zygote to adult; plant tips can be divided into three zones: cell division, cell elongation and cell differentiation. (p.7)
• Zone of cell division: actively dividing meristem cells through mitosis; new cells push older cells towards the elongation zone. (p.8)
• Zone of cell elongation: cells increase in size through osmotic water uptake and nutrient absorption; small vacuoles fuse into a large vacuole (vacuolation). (p.8)
• Zone of cell differentiation: cells reach maximum size, change shape and structure, and form permanent tissues such as epidermis, cortex, xylem and phloem. (p.8)
• Primary growth occurs after germination in all plants and elongates stems and roots. (p.10)
• Primary growth at shoot tips forms new leaves and shoots; at root tips the root cap is replaced by meristem cells. (p.10)
• Secondary growth occurs mainly in eudicots and a few monocots and increases the circumference or diameter of stems and roots. (p.10)
• In secondary growth of stems, the vascular cambium divides and forms secondary xylem inwards and secondary phloem outwards. (p.11)
• Thickened lignified xylem gives mechanical support; the epidermis cracks, and cork cambium forms cork cells that protect the stem from insects and pathogens. (p.11)
• Secondary growth of roots follows the same process as eudicot stems and makes the root thicker. (p.12)
• Annual growth rings in temperate plants reflect seasonal growth: spring xylem is bright and wide, summer xylem is dark and narrow; rings can be used to estimate age. (p.12)
• Monocots that undergo secondary growth include Dracaena sp., Aloe sp. and Agave sp. (p.13)
• Secondary growth provides stability, mechanical support, continuous xylem and phloem production, a thicker protective bark, and a longer lifespan. (p.13)
• Primary growth allows maximum elongation to absorb sunlight, and transports water, mineral salts and food between leaves and roots. (p.13)
• Primary and secondary growth in eudicots are similar in that both increase plant size permanently and involve mitosis; secondary growth is radial and produces annual rings and bark. (p.15)
• Plants with secondary growth have high economic value because they produce timber such as meranti and cengal, resin and oil, and commercial fruits. (p.16)

1.3 Growth Curves

• Plants are classified by life cycle into annual, biennial and perennial plants. (p.17)
• Annual plants complete one life cycle in a season or year and die after producing seeds, e.g. paddy, pumpkin and watermelon. (p.17)
• Biennial plants take two years and two growth seasons: vegetative growth in the first season, reproduction in the second, e.g. cabbage, carrot and silver cock's comb. (p.18)
• Perennial plants live more than two years and can flower and bear fruit many times, e.g. grass, hibiscus and mango. (p.18)
• Growth curve of annual plants is sigmoid: stage A decreasing dry mass, stage B increasing dry mass, stage C constant dry mass (mature), stage D decreasing dry mass due to ageing. (p.19)
• Growth curve of biennial plants is two combined sigmoid curves. (p.19)
• Growth curve of perennial plants is a series of small sigmoid curves, with high growth rate in spring and summer. (p.19)