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Plant Adaptations for Survival
6-2.4 Summarize the basic functions of the structures of a flowering plant for defense, survival, and reproduction.
6-2.8 Explain how plants respond to external stimuli (including dormancy and the forms of tropism known as phototropism,
gravitropism, hydrotropism, and thigmotropism).
6-2.9 Explain how disease-causing fungi can affect plants
Structures for Defense in Plants
Plants have structures for defense that protect them from outside threats. Without these defenses, the plant might be
harmed or could die.
5 Examples of Natural Defenses: Thorns, Poisons, Plant Structures, Dormancy, Tropisms
1. Thorns
Plants use thorns to deter animals from either eating the plant or getting
too close to it.
2. Poisons
Chemicals found in some plant leaves, fruit, or seeds can cause an animal that
eats it to die, be sick, or cause irritation.
Poisonous plants are sometimes brightly colored to advertise that it is harmful
3. Plant Structures for Survival
Plants have structures that allow them to survive in their habitats
when the conditions are not suitable.
The 4 structures that help a plant survive: Leaves, Stems, Roots, Seeds
□Leaves
Location of photosynthesis, respiration, and transpiration
- In some plants (like succulents) they also store water for the plant.
- Plants with a waxy cuticle are better adapted to keep the water in the leaf.
□Stems
Main support for the plant.
It holds up the leaves toward the sun for photosynthesis to occur.
Contains vascular tubes (xylem, phloem) for transportation of water and food.
Serves as a food storage location.
Different plants have stems that are best adapted to their environments.
□Roots
The larger the plant, the bigger the root system has to be.
Root Hairs
Taproot
Extend from roots, increase water
Act as anchors
absorption
to hold the
plant in the
soil.
Ex: Dicots
(carrots,
dandelion,
cacti)
Fibrous Root
Increase surface
area to absorb
more water and
nutrients.
Ex: Monocots
(grass, corn,
some trees)
□Plant Adaptations for Dry climates
-spines instead of leaves
-small surface area minimizes evaporation
-stems that can store water
-widespread root system for finding water
4. Dormancy
□Seed Dormancy
- The ability of a plant or seed to shut down to survive periods where the plant may die is called
dormancy.
- Dormancy in seeds is helped by the seed coat which protects the embryo from drying out and from
physical damage during the period of shut down.
- Dormancy ends when conditions are more suitable for the seedling to survive.
□Leaf and Branch Dormancy
- Dormancy in plants causes leaf and branch loss during periods of poor growing
conditions.
- Leaves return when there is no danger of poor growing conditions.
Ex: How does losing its leaves in the winter help a tree survive?
5. Tropisms
Tropisms are a natural tendency for a plant to respond toward or away from a stimulus
Are caused by hormones inside the plant cells
Examples: Thigmotropism, Hydrotropism, Phototropism, Gravitropism (geotropism)
Thigmotropism
▪ Growing or response to
touch
▪ Adaptation to protect
themselves from possible
harm or obtain resources.
Hydrotropism
▪ Tendency of a plant to
move towards or away
from water.
▪ The ability of a plant to
seek out water sources
ensures the plants survival.
▪ Best evidence is when
growth toward water is
stronger than
gravitropism.
Phototropism
▪ Ability of a plant to bend
towards or away from
light.
▪ If it is in the shade, it is
possible for a plant to bend
around the shade to find
the sun.
Gravitropism
▪Also known as Geotropism
▪Ability of a plant’s stem to
grow against gravity and the
roots to grow with gravity.
▪Its role is important
because germination usually
occurs in the dark,
underground.
Which type of root are the following pictures? Fibrous or Taproot?
1. __________________________
2. ___________________________
3. ____________________________
4. How long does adaptation usually take?
A. a decade B. an hour C. a few days D. centuries
5. What does it mean when a plant adapts?
A. It grows on the rainforest floor or under water
C. It grows giant leaves, and has very bright flowers
B. It changes itself to fit in better with its environment
D. It converts its surroundings into a kinder climate
6. Why do some plants in the rainforest have bright flowers and grow close to the ground?
A. To repel any extra rainfall
C. To keep animals and people away from them
B. To get as much sunlight on their leaves as possible
D. To attract birds, and insects for pollination
7. How have some rainforest plants adapted to receive enough sunlight?
A. By growing poisonous flowers
C. By growing giant, bright flowers
B. By growing giant, slippery leaves D. By growing long, deep roots
8. What are the two main types of roots?
9. What covers the leaves of succulents to protect them from water loss?
A. chlorophyll
C. poison
B. cuticle
D. stomata
Stimulus
Light
Water
Gravity
Touch
Tropism Response
10.
11.
12.
13.
14. Gravitropism occurs because seeds do not need _________________________ to germinate; therefore, the stems
and root must rely on gravity to direct them.
15. Plants have reproductive adaptations. Which of the following would be an adaptation for seed dispersal by wind?
A. apple seed
C. onion seed
B. dandelion seed
D. strawberry seed
16. Why would a root produce root hairs off of it?
17. Which root system is better adapted to absorb water and why?
18. What tropism would an ivy plant require to grow to full size?
Fungi
Belong to the Kingdom of Fungi
Are heterotrophs
 Absorb nutrients from the living or dead
organisms they grow on
 Many grow in or on other organisms
 Mold: often grows on old food
 Mushrooms: often grows on trees
Disease-Causing Fungi
 Can eventually kill the plant it infects
 Can cause losses in food crops
 Disease-Causing Fungi Examples
– Grain mold, Wheat rust, Corn smut
– Diseases also affect rice, cotton, rye,
and soybeans
Helpful Fungi
 Helpful as decomposers
– breaks down decaying matter
 Can be made into medicines
– Penicillin fights bacteria
 Are food
– Mushrooms, truffles
19. True or False: Fungi do not make their own food.
20. How does fungi get the food that it eats?
21. Why are some disease-causing fungi dangerous for plants?
22. True or False: All fungi are bad or dangerous.