Chapter 23 2 Roots Describe the two main

Chapter 23 -2: Roots Describe the two main types of roots Identify the tissues and structures in a root Describe the different functions of roots

Root types • The two main types of roots are: – Taproots (found mainly in monocots) • The primary root is long and thick while the secondary root s are small • Carrots, dandelions, beets, radishes, oak and hickory trees have taproots – Fibrous roots (found mainly in dicots) • All the roots branch out and are similar in size • Grasses have fibrous roots

Root Tissues • Roots contain cells from four tissue layers: – Dermal tissue (outer most tissue layer) – Vascular tissue (contains the xylem and phloem) – Ground tissue (everything else) – Meristemic tissue (where new undifferentiated new cells are formed by mitosis; found at the root tips is called apical meristem)

Root Structure • A mature root has an outside layer of epidermal cells and a central cylinder of vascular tissue • Between these two tissues lies a large area of ground tissue or cortex • At the tips is the apical meristem. This is where the root will elongate (grow in length) • The root cap protects the newly formed cells as the root pushes through the ground

Root Functions • Roots have three functions: – Anchor the plant into the ground – Take in nutrients • Root hairs have active transport protein pumps that actively pump in the nutrients from the soil through the epidermis to the cortex and traps it in the vascular cylinder – Absorb water • As the roots are pumping in the nutrients the concentration of nutrients becomes higher in the root tissues causing water to “follow” those nutrients into the roots.

Stem Functions • Hold leaves up to the sunlight • Transport substances between the leaves and the roots

Stem Growth Primary Growth Secondary Growth • Primary growth occurs only at the end of plants (makes them taller) • Primary growth involves apical meristem tissues • Secondary growth is a pattern in which stems increase in width • Secondary growth involves lateral meristematic tissues – Vascular cambium – which produces new xylem and phloem – Cork cambium – which produces the outer covering of the stem (bark)

Chapter 23 -4 Leaves Describe how the structure of a leaf enables it to carry out photosynthesis Describe how gas exchange takes place in a leaf

Basic Leaf Parts

Cross-section of a leaf

Carrying out Photosynthesis • Carbon dioxide enters the leaf and oxygen exits the leaf through the stomata in the underside of the leaf. Guard cells control the opening and closing of the stomata (this regulates how much water is lost and gas is exchanged) • The mesophyll layers (spongy and palisade) contain chloroplasts. The palisade captures most of the sunlight for photosynthesis