Transcript Seed Plants

Seed Plants
Chapter 27
Seeds are ‘better’ than spores

Seed contains a multicellular young plant


Seeds contain a food supply


After germination the plant is nourished until selfsufficient
Seeds are protected by a seed coat


Root, stem, and at least one leaf are already formed
Seeds live for extended periods at a reduced metabolism
until conditions for germination are adequate
Seed plants are the dominant plants in most
terrestrial ecosystems
Major characteristics of seed plants




Vascular tissue: xylem and phloem
Alternation of generations
Two groups based on seed structures
Gymnosperms



An ovary wall does NOT surround the ovule
Pine, spruce, fir, hemlock, gingko
Angiosperms


Produce seeds within a flower/fruit
Very diverse group
Gymnosperms




Name means ‘naked seed’
Seeds are totally exposed or carried on the
scales of cones
The ovary wall does not surround the ovule
Four phyla:



Conifers
Ginkgo and cycads
Gnetopytes
Conifers





Largest and most familiar group
Pines, spruces, firs, hemlocks
All are woody
Leaves are needles and usually evergreen
Most are monoecious



Separate male and female reproductive parts (cones) on the
same plant
Wide range – from arctic to tropics
Used for building materials, resins, and
landscaping/decorating
Conifer species,
clockwise from
top-left:
Western red cedar,
Douglas fir, spruce,
and lodgepole pine.
The conifer life cycle

Male cone – pollen cone



Female cone – seed cone



Produce pollen grains – each with 4 cells and large air sacs
Pollen grains are spread by wind
Larger and more noticeable
Pollination – occurs in the spring
Fertilization – occurs about 15 months after
pollination; seeds take another few months to mature
Other gymnosperms

Cycads:



Ginkgo:



Most ancient species are now extinct
Dioecious – separate male and female plants
Only one living species
Leaf extract has been used to increase blood flow to the
brain and may aid memory
Gnetophytes:


Have more efficient water conducting cells
Ephedrine – stimulates the heart and raises blood pressure
Clockwise from top left:
Cycad, gingko,
gnetophyte
Angiosperms



Most successful plants today
Very important to humans
Divided into two classes:

Monocots – have a single seed leaf




Herbaceous
Narrow leaves with parallel veins
Flower parts in multiples of 3
Dicots – have two seed leaves



Either herbaceous or woody
Broad leaves with net venation
Flower parts in multiples of 4 or 5