Evolution of seed plants

Question 1

What were the first plants to develop seed-like structures?

Answer 1

Seed ferns. Appeared 400 mya but are extinct

Question 2

What were the traits of progymnosperms?

Answer 2

Had spores instead of seeds, may have evolved from seed ferns. Branched off 390 mya

Question 3

When did the radiation of gymnosperms happen?

Answer 3

250 mya. They took over the world from the seedless vascular plants after the Permian extinction

Question 4

When did angiosperms appear in the fossil record?

Answer 4

130-150 mya

Question 5

When did pollen first appear in the fossil record?

Answer 5

250 mya

Question 6

What are the 2 reasons why pollen was a huge competitive advantage?

Answer 6

1. No longer reliant on water for gamete exchange, pollen can go a lot further than just the neighbours, which increases genetic diversity
2. Sperm is very easy to kill, and pollen isn’t

Question 7

What are the 3 components of a pollen grain?

Answer 7

Generative cell
Tube cell
Pollen wall

Question 8

What does the generative cell of pollen do?

Answer 8

The sperm cell that will fertilize the egg

Question 9

What does the tube cell of pollen do?

Answer 9

Transports the sperm cell to the egg

Question 10

What does the pollen wall do?

Answer 10

Mechanical stability, gas exchange, and provides a chemically inert environment

Question 11

What is the pollen wall made of that makes it so strong?

Answer 11

Partly made of sporopollenin, which is completely inert and basically indestructible

Question 12

Why are seeds an adaptive advantage over spores?

Answer 12

Embryo is protected and encased in a seed, and can be transported far from the parent plant. Seeds also last a lot longer than spores

Question 13

Where does the embryo get nutrients from in a gymnosperm seed?

Answer 13

Female gametophyte tissue

Question 14

What are 2 ways seeds are dispersed?

Answer 14

Wind: often have modifications to increase drag

Animal based

Question 15

How developed is the cuticle of seed plants?

Answer 15

Very complex and well developed. Covers the hypodermis. Much more complex than Monilophytes

Question 16

How many gymnosperms and angiosperms show secondary growth?

Answer 16

Only present in woody angiosperm species, but is in almost all gymnosperms

Question 17

How is having secondary growth an advantage for gymnosperms and angiosperms?

Answer 17

They can grow outwards to expand their stems, which allows them to grow taller and opens up possibilities for mechanical support

Question 18

What 7 traits are common to both gymnosperms and angiosperms?

Answer 18

Pollen is all that remains of the microgameteophyte
Fertilization occurs via the pollen tube
Use seeds for dispersal
Lacks antheridia
Heterosporous
Secondary cell walls
Woody species have secondary growth

Question 19

How are gymnosperms and angiosperms different in terms of ovule placement?

Answer 19

Gymnosperms: ovules are exposed
Angiosperms: ovules are enclosed in the carpel

Question 20

How are gymnosperms and angiosperms different in terms of pollination?

Answer 20

Gymnosperms: direct pollination by the pollen landing directly on the ovule. Often wind pollinated
Angiosperms: indirect pollination by the pollen landing on the stigma then the pollen tube growing down the style to fertilize the ovule. Often animal pollinated

Question 21

How are gymnosperms and angiosperms different in terms of fertilization?

Answer 21

Gymnosperms: single fertilization. One generative cell fertilizes the egg and the female gametophyte tissue provides nutrition to the embryo
Angiosperms: double fertilization. The generative cell splits into two before fertilizing the egg, one will fertilize the embryo and the other fertilizes the polar nuclei. The endosperm provides nutrition to the embryo

Question 22

How are gymnosperms and angiosperms different in terms of the megagametophyte?

Answer 22

Gymnosperms: larger megagametophyte with 2 archegonia each with one egg. Completely parasitic on the sporophyte at all life cycle stages
Angiosperms: 7 celled, 8 nucleated with no archegonia. Has a large cell in the middle with 2 polar nuclei, 3 antipodal cells, 2 synergids, and one egg cell

Question 23

How are gymnosperms and angiosperms different in terms of fruits?

Answer 23

Gymnosperms: no fruits
Angiosperms: fruit