1. Bellwork: How can seeded plants reproduce without standing water
Bellwork: How can seeded plants reproduce without standing water? Describe their general life cycle

2. Seed plants
Section 22.3

3. What is a seed?
A plant embryo and food supply encased in a protective coating
Living plant is diploid
Early development stage of sporophyte stage of plant life cycle

4. The first seed plants First fossils date bake to 360 million years ago
Several evolutionary stages chart the development of the seed
DNA evidence suggests all seed plants share a common ancestor
Key evolutionary steps:
No standing water required for fertilization
Through reproductive process involving cones or flowers
Pollination
Embryos in seed

5. What is the relationship between gametophyte and sporophyte in seed plants?
Male and Female gametophyte grow and mature directly within the sporophyte
Gametophytes either develop in cones or flowers
Two groups exist on the basis of which structures are present
Gymnosperms – seeds on scales of cones
Angiosperms – seeds in flowers
Layer of tissue to protect the seed

6. What is the role of pollen?
Entire male gametophyte is contained within a pollen grain
Sperm do not swim through water
Carried by wind or insects to fertilize eggs
Process called pollination

7. How does a seed form?
After fertilization, zygote in seed grows into a tiny plant
Embryo will stop growing whilst it is small and contained within a seed
Can remain this way for weeks, months or years
Seed coat provides protection
Can survive long periods of bitter cold, extreme heat or drought
Embryo will begin to grow again when conditions are once again right
Uses nutrients from stored food supply until it can carry out photosynthesis on its own

8. How does fertilization take place in gymnosperms?
Name means – ‘naked seed’
Seeds exposed on scales of cones
Cones are produced by mature sporophyte plant
Two types of cones produced – pollen cones and seed cones
One pollen grain is entire male gametophyte – one haploid nuclei will divide to produce two sperm cells
Familiar seed cones/female cones produce female gametophytes
Larger than pollen cones
Two ovules found near base
In ovules meiosis produces female gametophytes that contain hundred and thousands of egg cells – when mature each gametophyte contains a few large eggs cells ready for fertilization

9. The life cycle continued
Entire cycle takes two years to complete
Male pollen carried by wind to female cones
Pollen grains caught in sticky secretion on the scales of the female cone
Pulled into the ovule
No need for standing water
Pollen grains are able to produce pollen tubes which contains two haploid sperm nuclei
One fertilizes the egg, the other disintegrates
Diploid zygote produced
Grows into embryo
Encased to form a seed
Scattered by wind to form a new plant

10. The life cycle overviewed

11. Key points questions
What adaptations allow seed plants to reproduce without water?
What is a Gymnosperm
How does fertilization of a Gymnosperm take place?