Structures and Functions in Plants Roots, Stems, and Leaves

Specialized Plant Cells There are three types of cell found in plants that are arranged differently in roots, stems, and leaves. Parenchyma Collenchyma Sclerenchyma

Parenchyma Loosely packed, cube-shaped or elongated cells with large central vacuoles Involved with many metabolic functions including photosynthesis Usually form the bulk of nonwoody plants Alive at maturity

Collenchyma Thicker cell walls Provide support for the plant Usually in founds in strands Celery has a lot of collenchyma cells Alive at maturity

Sclerenchyma Thick,even,rigid cell walls Support and strengthen in areas of plant no longer growing Dead at maturity This is FIBER! The gritty texture of the pear fruit is due to sclerenchyma cells!

Plants Also Have Tissue Systems Plants cells work together to form three tissue systems: dermal, ground, and vascular. These tissue systems organize to produce the three organs of a plant: roots, stems and leaves.

Dermal Tissue Ground Tissue Vascular Tissue Primary function is absorption and protection. Parenchyma cells. Forms the outside covering of plants Epidermis and cuticle Ground Tissue This consists of all three types of cells. Mostly parenchyma, some collenchyma and few sclerenchyma Primary function is storage and support. Vascular Tissue Primary function is transport and support. Xylem and phloem

Growth Occurs in Meristem Apical Tips of roots and shoots Growth in length Lateral Occurs in gymnosperms and most dicots Growth in diameter Intercalary Located above the bases of leaves and stems

Roots Tap Fibrous Adventitious

Primary Growth in Roots Roots increase in length through cell division, elongation, and maturation in the root tip. A root cap covers the apical meristem. It produces a slimy substance allowing the root to move easily through the soil. Root hairs are extensions of the epidermis that increase surface area.

Secondary Growth in Roots This occurs in gymnosperms and dicots. The vascular core of a primary root is surrounded by the pericycle. The pericycle produces lateral roots.

Root Functions Anchor the plant in the soil Absorb water and minerals 13 minerals are required for normal growth Adapted to store carbohydrates Usually stored as starch and stored in parenchyma cells Potatoes, sweet potatoes, carrots, turnips

Modified Roots

Monocot vs Dicots Roots epidermis endodermis xylem phloem Vascular tissue matures to form the innermost cylinder of the root. In the dicot, the xylem forms an X and the monocot has a prominent endodermis. The cortex is between the epidermis and endodermis. The cortex and the endodermis compose the GROUND TISSUE.

Stems There are many differences in stem shape and growth that are the results of adaptations to the environment. Stems have a more complex structure than roots. Stems grow in length at the tips and grow in circumference through lateral meristem.

Stem Structures

Stems are divided into segments called internodes. A node is at the end of each internode. At the point of attachment, each leaf has bud. A bud is capable of developing into a new shoot. The bud has apical meristem enclosed in special leaves called bud scales. At the tip of each stem there is usually a terminal bud. Each spring when growth resumes, the terminal bud opens.

Primary Growth in Stems Apical meristem gives rise to all three types of tissue. In gymnosperms and dicots, ground tissue forms the cortex and pith. Pith is located in the center of the stem. In monocots, the ground tissue does not separate into pith and cortex.

Monocot / Dicot Stems Monkey faces

Secondary Growth in Stems is Called Wood Summerwood Sapwood (light) Springwood Annual ring Heartwood Bark-protective outer covering composed of cork, cork cambium and phloem

Functions of Stems Function in transport and storage of nutrients. Translocation is the movement of food in the phloem. Pressure-flow hypothesis (carbohydrates are actively transported and water moves by osmosis) Transpiration is water loss (cohesion-tension theory)

Storage of Water and Nutrients Abundant parenchyma cells in the cortex provide plants with ample storage. Cactus stems are specialized for storing water. Sugar-cane stores large amounts of sucrose. Potatoes store starch.

Leaves Most leaves are thin and flat, an adaptation that helps a plant capture sunlight for photosynthesis. Leaves exist in many variations that reflect adaptations to environmental conditions.

Leaf Adaptations Tendrils – coiled specialized leaves to aid a climbing vine ( some may be modified stems – grapes) Carnivorous plants – pitcher plant and venus fly trap – leaves function as food traps Spines- modified leaves that protect the plant. Spines are small and nonphotosynthetic. In a cactus, spines reduce transpiration.

Leaf Structures blade stipules petiole vein midrib

Leaves are Either Simple or Compound Simple leaves

A compound leaf consists of several, separated segments called leaflets. The leaflets are usually grouped in pairs around the elongated rhachis that corresponds to the midrib of a normal leaf.

Leaf Arrangement

Vein Patterns In parallel - veined leaves, the veins run parallel to each other. This condition is characteristic of the monocotyledoneae. Pinnately netted - veined leaves have a single primary vein or midrib, from which smaller veins branch off, like the divisions of a feather. Palmately netted- veined leaves have several principal veins radiating from the base of the leaf blade, as in Acer rubrum (red maple).

Parts of a leaf Stomata palisade layer spongy layer veins chloroplast thylakoids grana stroma

Leaf Functions Photosynthesis Limitations – insufficient water due to transpiration. A corn plant losses 98% of water absorbed by roots through transpiration.

Benefits of Photosynthesis 1. The oxygen in the air comes from photosynthesis. The plants continue to replenish the oxygen in the air. 2. All of our food comes directly or indirectly from photosynthesis.