Plant Structure, Growth, and Angiosperm Reproduction
Plant organs
Roots (part of the root system)
Stems (part of shoot system)
Leaves (part of the shoot system)
The roots are an organ that anchor a vascular plant into the soil and also function to absorb water and minerals, also storing carbohydrates
Taproot system
Fibrous root system
Single main vertical root which penetrates deep into the soil and prevents the plant from falling over
Lateral roots responsible for absorption
Helps plant grow tall
Mat of thin roots that spread below surface of the soil
Many small roots spread out from stem
May be adventitious: growing in an unusual location
Root hairs- finger-like extensions of root epidermal cells that increase surface area for absorption
The organ to which leaves are attached whose main function is elongation and orientation of the shoot in a way to maximize photosynthetic capability of the leaves
Also elevates reproductive structures to maximize dispersal range
Has a system of alternating nodes and internodes
Nodes: points where leaves are attached
Internodes: stem segments in between nodes
Apical bud: bud at the tip of a plant stem (terminal bud) that is composed of developing leaves and compact series of nodes and internodes (grows vertically)
Axillary bud: structure that has the potential to form a lateral shoot of branch, which forms in the angle formed between a leaf and a stem (grows laterally)
This is the main photosynthetic organ of the plant- responsible for photosynthesis, gas exchange, heat dissipation, and defense against pathogens and herbivores
Consists of a flattened blade and a stalk (petiole) that joins the leaf to the stem at a node
Leaves have vascular tissue (veins) which transport supplies for photosynthesis toward the leaf and the products away to the rest of the plant
Great variation exists in leaf morphology
Vital structures
Stomata- allow for gas exchange
Guard cells- regulate opening and closing of stomata (impact water loss)
Mesophyll- contains specialized cells for photosynthesis
Vascular tissue- transport nutrients and products of photosynthesis
Major tissues in plants
Vascular tissue system
Ground tissue system
Dermal tissue system
This is the plants outer protective covering that is its defense against pathogens and physical damage
Non-woody plants: have epidermis (tightly packed cells) and cuticle (waxy outer covering that prevents water loss)
Woody plants: have periderm instead of epidermis in older regions of stems and roots which provides more protection
Facilitates transport (water and minerals) through plant as well as provide mechanical support
2 tissue types
Xylem: conduct water and dissolved minerals from root to shoot
Phloem: transport sugar to roots and growth sites
Stele: vascular tissue of a root or stem
Vascular cylinder in root (solid central bundle of tissue)
Vascular bundles in stems and leaves (separate xylem and phloem)
Includes tissues that are neither dermal nor vascular
Pith: ground tissue internal to vascular tissue
Cortex: ground tissue external to vascular tissue
Contains cells that function in photosynthesis, short distance transport, storage, and support
Primary growth
This type of growth occurs in all plants (woody and non-woody)
Primary growth occurs in the apical meristems at the tip of shoots and shoots and axillary buds of shoots
Enable growth in length- producing almost all of the plant body in non-woody plants
Apical dominance occurs when an active apical bud inhibits growth from nearby axillary buds through plant hormones
If an apical bud is removed, an axillary bud will grow a lateral shoot
If an apical bud is removed and plant hormones are applied at the site of removal, the axillary bud will not grow
Secondary growth
This type of growth only occurs in woody plants
It occurs in the lateral meristems that enable growth in thickness
The vascular cambium adds layers of vascular tissue (secondary xylem and phloem)
The cork cambium replaces the epidermis with thicker, tougher periderm
Consists of the tissues produced by vascular and cork cambium
Increases diameter of stems and roots- mostly occurs in eudicots and gymnosperms but rarely monocots
Primary and secondary growth occur simultaneously
Pollination: act of placing pollen (has male gametophyte) on the stigma of the carpel
During this process, the male gametophyte then travels to the gametophyte (inside embryo sacs in the ovule)
Plants tend to transfer pollen to a different flower
3 types of pollination:
Abiotic pollination (ex. wind)
Biotic pollination: living organisms pollinate other plants (insects, bees, bats, birds, etc.)
Self-fertilizing: in some crop plants (ensures every ovule develops into a seed)
Combine self pollen and ovule to form a zygote (potentially detrimental because it does not increase genetic diversity)
Some angiosperms have evolved mechanisms to prevent self-fertilization
Angiosperm reproduction
Forming the male gametophyte
Process of pollination
Forming the female gametophyte
Double fertilization
In the megasporangium of each ovule (in the ovary), the megasporocyte undergoes meiosis to produce 4 megaspores
One megaspore survives to become the female gametophyte (embryo sac)
Embryo sac consists of: antipodal cells, polar nuclei, synergids, egg (haploid)
On the anther, each microsporangium contains microsporocytes that undergo meiosis each to produce 4 haploid microspores
The microspore undergoes mitosis to produce the male gametophyte (pollen grain, generative cell and tube cell)
The generative cell divides to form 2 sperm which pass into the tube cell during gametophyte maturation
The pollen grain is transferred to the surface of the stigma
Tube cell produces pollen tube which delivers sperm to the female gametophyte
1 sperm fertilizes the egg to form the zygote
1 sperm combines with 2 polar nuclei to form the 3n endosperm
After double fertilization
The zygote develops into the embryo (which is packages with food into seed)
The seed may be enclosed by fruit
Asexual vs. sexual reproduction in plants
Many angiosperm species can do both
Asexual reproduction- the formation of offspring from a single parent without the fusion of gametes
Occurs by budding, division of a single cell, or division of a whole organism into multiple parts
Offspring generally genetically identical to the parent
Also called vegetative reproduction
Predominant mode of reproduction for some species of angiosperms
Sexual reproduction- formation of offspring from two parents by fusion of gametes
2 forms:
Fragmentation- detached fragment from the plant that can become a whole new plant
Apomixis- plants may produce seed without pollination or fertilization
Ex. Aspen tree in Utah
Ex. dandelions
Increases genetic diversity
Pollen grain (sperm) fertilizes the egg to produce the zygote
Offspring not identical genetically to the parents