Transcript young leaf
Plant Growth AP Biology Growth in Animals Animals grow throughout the whole organism Many regions & tissues at different rates Growth stops when a certain size or development is reached Called determinate growth. AP Biology Growth in Plants Specific regions of growth: meristems Perpetually embryonic tissue Cells can divide indefinitely. Called indeterminate growth. AP Biology Growth in Plants regenerate new cells apical shoot meristem growth in length primary growth apical root meristem growth in length primary growth lateral meristem growth in girth secondary growth AP Biology Apical meristems AP Biology shoot root Root structure & growth AP Biology protecting the meristem Shoot growth Apical bud & primary growth of shoot Region of stem growth Lengthens the shoot by mitosis and cell division. Tip of shoot = Apex protecting the meristem Young leaf primordium Apical meristem Older leaf primordium Lateral bud primordium AP Biology Vascular tissue Primary xylem Growth in woody plants Primary phloem Woody plants grow in Epidermis height from tip Lateral meristems primary growth apical meristem Woody plants grow in diameter from sides secondary growth lateral meristems Primary phloem Secondary phloem Secondary Primary xylem xylem vascular cambium makes 2° phloem & 2° xylem cork cambium makes bark Annual AP Biology growth layers Bark Secondary growth Secondary growth growth in diameter thickens & strengthens older part of tree cork cambium makes bark growing ring around tree vascular cambium makes xylem & phloem growing ring around tree AP Biology Vascular cambium Why are early & late growth different? Phloem produced to the outside Xylem produced to the inside bark cork cambium phloem xylem vascular cambium AP Biology late early last year’s xylem cork cambium Woody stem How old is this tree? vascular cambium late early 3 2 1 xylem phloem AP Biology bark Tree trunk anatomy tree girdling What does girdling do to a tree? AP Biology Aaaargh! Murderer! Arborcide! Where will the carving be in 50 years? AP Biology PLANT HORMONES A. Are chemical signals that coordinate different parts of an organism. B. Require only minute amounts. C. Produced by 1 part of plant body. D. Transported to another part E. Binds to specific receptor F. Triggers response in target cells and tissues. AP Biology Examples of Plant hormones: auxin gibberellins abscisic acid ethylene and more… AP Biology Auxin (indole-3 acetic acid or IAA) Effects controls cell division & differentiation phototropism growth towards light asymmetrical distribution of auxin cells on darker side elongate faster than cells on brighter side AP Biology Auxin (indole-3 acetic acid or IAA) Effects Apical dominance Prevents axillary buds from growing. These auxins are produced by meristem in shoot apex. AP Biology Gibberellins Family of hormones over 100 different gibberellins identified Effects stem elongation fruit growth seed germination AP Biology plump grapes in grocery stores have been treated with gibberellin hormones while on the vine Animal vs. Plant Responses Comparing responses to stimuli of plants and animals: A. Animals – Respond to stimuli by changing behavior. 1. Move toward positive stimulus 2. Move away from negative stimulus AP Biology B. Plants – Respond to stimuli by: Adjusting growth and development Plants adjusting their directional growth responses to directional external stimuli (such as light or gravity) are called tropisms. Response to light is phototropism. Response to gravity is called gravitropism. Growth toward a stimulus is a positive tropism. Growth away from a stimulus is a negative tropism. AP Biology Auxin influences gene expression in phototropism. Light is absorbed by photoreceptor proteins called phototropins. Phototropins change conformation and bind to receptors within the cell. Receptors control specific genes transcribing plasma membrane proteins which transport auxin. AP Biology