Plant Reproduction and Growth: Phloem, Xylem, and Tropisms
Phloem
The phloem moves food substances that the plant has produced by photosynthesis to where they are needed for processes such as:
- Growing parts of the plant for immediate use
- Storage organs such as bulbs and tubers
- Developing seeds
Asexual reproduction generates offspring that are genetically identical to a single parent.
Step 1: After pollen has landed on the stigma, it goes a pollen tube down through the style to the ovary.
Step 2: The nucleus of the pollen grain travels down the pollen tube and fertilizes the ovule in the ovary.
Step 3: The fertilized ovule develops into a seed. The seed contains the plant embryo, which contains genetic material from both parents. The ovary develops into the fruit.
Xylem and Phloem
- The xylem is a tissue that transports water and minerals from the roots up the plant stem and into the leaves.
- Xylem consists of dead cells. The cells that make up the xylem are adapted to their function:
- They lose their end walls so the xylem forms a continuous, hollow tube.
- They become strengthened by a substance called lignin, which gives strength and support to the plant.
Asexual reproduction: Only one parent and no mixing of materials.
Sexual Reproduction: Fusion and genetic variation.
- Gamete: Sex cell (haploid)
- Zygote: Fertilized egg (diploid, 2n)
- Clone: A genetically identical organism
Organisms that can reproduce sexually and asexually:
- Most fungal species
- Strawberry plants
- Aphids
- Some species of starfish
- Jellyfish
Feature
| Insect-pollinated flowers | Wind-pollinated flowers |
|---|---|
| Petal: Often large and brightly colored | Petal: Small, inconspicuous or absent |
| Nectar and scent: Insects feed on nectar and are attracted by the scent | Nectar and scent: None |
| Stamen: Enclosed in flower | Stamen: Long filaments with anthers hanging outside when ripe |
| Pollen: Small with surface features to stick to insects and stigma | Pollen: Large with smooth surface to float through the air |
| Stigma: Enclosed in flower to catch pollen | Stigma: Feathery and outside the flower to catch pollen in the air |
Introduction to Flower Structure
- Stigma: Part of the female reproductive system of a flower
- Anther: Contains the pollen
- Filament: Supports the pollen anther
- Style: Supports the stigma and connects it to the ovary
- Ovary: Enlarged portion of the pistil, the female organ of a flower
Role of Auxin
- Auxin is a plant hormone that chemically affects plant growth
- Auxin causes elongation (growth)
- Auxin is produced in the tips of roots and shoots
- Light causes auxin to move to the shadier side of the plant
- Shadier side of the plant elongates (grows)
- Shoot bends towards the light
Geotropic Response
- Positive geotropism: Roots grow downwards towards gravity
- Negative geotropism: Stem grows upwards against gravity
Phototropic Response
- Positive phototropism: Leaves/stem grow towards light
- Negative phototropism: Roots grow downwards away from light
- A positive response is towards a stimulus and a negative response is away from a stimulus
Tropisms
Plants respond to stimuli with tropisms such as geotropism and phototropism in roots and stems. Auxins are plant hormones that regulate growth towards light. Roots are negatively phototropic and positively gravitropic. Plants respond to stimuli like light intensity, humidity, and temperature with tropisms.
C6 H12 O6 + 6O2 → 6CO2 + 6H2O
Respiration releases energy. Xylem and phloem transport water, minerals, and sugars throughout the plant. Excretory products in plants include carbon dioxide and water.
Transpiration
Plant excretion occurs through the stomata of leaves and lenticels of stems.
The role of the green pigment chlorophyll is to absorb light energy for photosynthesis. Photosynthesis converts light energy into chemical energy in the form of glucose and oxygen.
Thermal Regulation is the control of internal body temperature. Homeostasis maintains stable internal conditions for proper function. The body uses mechanisms to cool down or conserve heat. It is important for enzymes to function at optimal temperatures.