Transcript Plant Adaptations & Plant Tropisms

Roots, Stems, & Leaves
Roots
2 Main Types:
1. Tap Roots
•
•
long & thick primary root with small secondary
roots
Found in dicots like oaks, carrots, beets,
dandelions
2. Fibrous roots
•
•
•
Branching with no single larger root
Mainly found in monocots
Extensive root systems help prevent topsoil
erosion
Root Structure & Function
Structures:
• Epidermis - both protects and absorbs
• Root hairs - penetrate soil & provide larger
surface area for absorption
• Cortex - Ground tissue between epidermis &
vascular cylinder
• Endodermis - layer that surrounds vascular
cylinder
Function
• Roots anchor the plant in the ground and
absorb water & dissolved minerals from
soil
Leaves
Characteristics:
• Main organs of photosynthesis
• Blade – thin, flattened sections for
collecting sunlight
• Petiole – stalk which attaches blade to stem
Guard cells
One of the paired epidermal cells that control
the opening and closing of a stoma in plant
tissue.
Stems
Functions:
• Produce leaves, branches, & flowers
• Hold leaves up to sunlight
• Transport substances between roots &
leaves
Stem Structure
• Stems are composed of dermal, vascular, &
ground tissue
• Nodes - where leaves are attached
• Internode - regions in between nodes
• Buds - undeveloped tissue that can produce new
stems & leaves; found where leaves attach to
nodes
Specialized Stems
Stems that store food and can remain dormant
for a time
• Tuber – usually grows underground, stores food (potato)
• Bulb – central stem surrounded by short, thick leaves
(onion)
• Corm – similar to bulb but stem is thickened to store food
(gladiolus flower)
• Rhizome – horizontal underground stem that can form
new shoots (ginger)
Plant Adaptations & Plant Tropisms
Plant Adaptations
• Dormancy – period during which growth
& activity decrease or stop
Plant Adaptations
Aquatic plants must tolerate mud nearly
devoid of oxygen
• Tissues with air-filled spaces for O2 to
diffuse
• Seeds often float and grow quickly
Plant Adaptations
Xerophytes - desert plants
• Root systems spread out for long
distances
• Leaves may be reduced to spines;
photosynthesis occurs in stems, which
also store water
Plant Adaptations
Carnivorous plants – live in bogs with little
nitrogen
• Use specialized leaves to trap & digest
insects to meet nutritional needs
• Pitcher plants - drown insects in
specialized leaves
• Sundews - trap insects with sticky
secretions
• Venus’ flytrap - has leaves that snap shut
Plant Adaptations
Parasites & Epiphytes – extract water &
nutrients from a host plant
• Parasites harm the host
• Epiphytes grow on bodies of other plants
but gather their own water & produce
their own food
– Ex: Spanish moss, bromeliads, many orchids
Plant Adaptations
Chemical defenses – manufacture poisons,
insect hormones, etc. that effect
animals/insects
Plant Tropisms
Plant Tropisms - responses of plants to external
stimuli
• Gravitropism – stems grow up & roots grow
down
• Phototropism – plants grow toward light
• Thigmotropism – response to touch – vines &
climbing plants wrap around support structures
Plant Hormones
1. Auxins – cause of phototropism
• Stimulate cell elongation
• Higher concentration on shaded side of the plant
causing stem to elongate and bend
-- Cause of gravitropism
• higher concentration on lower part of root stem
inhibit cell growth, causing root to grow
downward.
• Help move root through the soil and around
objects in the soil
Plant Hormones
2. Cytokinins – produced in growing roots
and in developing fruits and seeds.
• Cause dormant seeds to sprout
• Cells grow thicker
3. Gibberellins – growth promoting
• Increase size of stems and fruits
4. Ethylene – stimulates fruit to ripen