Plant Structure and Function Roots, Stems, and Leaves
What is a Plant? Plants are living things that have: roots, stems, and leaves (some have flowers) Plants are made of cells that have cell walls, a large central vacuole, and chloroplasts Chloroplasts contain a green pigment called chlorophyll that play a role in photosynthesis
Photosynthesis 6H 2 O + 6CO 2 ----------> C 6 H 12 O 6 + 6O 2
Life on Land Adaptations! Problem Drying Out Making Food Reproduction Gravity & Support Getting water & nutrients Solution Waxy cuticle, stomata Formed leaves Develops spores & seeds Bark (cork) & vessels; cell walls (cellulose) Roots & vessels
Protections and Support - Leaf
Leaf Structure Cuticle: A waxy covering on the upper and lower surface that helps to prevent water loss from the leaf. Mesophyll: Palisade Cells Upper surface of leaf cuticle epidermal cell The middle area of the leaf. Composed of palisade cells and spongy cells. Both types of cells contain many chloroplasts. The palisade layer is the primary photosynthetic layer of the leaf. Spongy Cells Lower surface of leaf cuticle
Leaf Structure guard cell stoma CO 2 in O 2 out H 2 O out Stomata: 1. Pores on the underside of the leaf through which carbon dioxide enters the leaf and oxygen exits the leaf. 2. The stoma is the opening into the leaf. 3. Guard cells are found on either side of a stoma. Their function is to open and close the stoma. 4. This is a source of water loss from the plant. 5. The stomata must open to let carbon dioxide into the leaf, but when they are open, water will escape the leaf. 6. Stomata are usually only found on the lower surface. This helps to reduce water loss.
Leaf Structure Vascular bundle (vein) glucose H 2 O Vascular Bundle (Vein): 1. Contains Xylem and Phloem. 2. Xylem carries water up the plant. Water is brought to the leaf through the xylem. guard cell stoma CO 2 O 2 3. Phloem carries food down the plant. The glucose being made will exit the leaf through the phloem and will be carried to other parts of the plant. H2O
There will have to be trade-offs or compromises between photosynthesis and the prevention of excessive water loss. The Water Loss Dilemma The number one problem that land plants face is dehydration. Plants must open their stomata to let in the carbon dioxide that is required for photosynthesis. But anytime the stomata are open, there will be excessive water loss through the stomata. On a hot, dry day, most plants will close their stomata to conserve water. But with the stomata closed, photosynthesis will drastically slow down since no carbon dioxide can enter the leaf.
Classification VASCULAR: have tube-like structures that carry water, nutrients, and other substances through the plant NONVASCULAR: do not have these tube-like structures and use other ways to move water and substances Binomial Nomenclature: two word system of naming things, e.g., Quercus alba = white oak
Seed Plants Have leaves, roots, stems, and vascular tissue; produce seeds Gymnosperms and Angiosperms Leaf made up of different layers of cells Waxy cuticle Epidermis (Stomata surrounded by guard cells) Palisade layer most food produced here Spongy layer veins containing vascular tissue found here Lower Epidermis
Stems and Roots Herbaceous stems: soft and green Woody stems: hard, rigid Roots have vascular tissue in which water and dissolved substances move from the soil through the stems to the leaves; roots also act as anchors Roots can store food, e.g., carrots, beets Absorb oxygen for use in respiration ~ making energy for the plant s cells
Vascular Tissue Xylem: hollow, tubular cells stacked one on top of the other to form a structure called a vessel; transport water and dissolved substances Phloem: tubular cells that are stacked to form structures called tubes; move food from where it is made to other parts of the plant where it is used or stored Cambium: between xylem and phloem; produces new xylem and phloem
Life Cycles of Angiosperms Biennials: complete their life cycles within two years Annuals: complete their life cycles in one year Perennials: take more than two years to grow to maturity