gymnosperms

Question 1

what are some significant features of
the evolution of seeded plants

Answer 1

1) the evolution of an ovule and seed
2) the female gametophyte being retained within the mother sporophyte
3) the ovule developing into a seed
4) replacing a spore with a seed as a unit of dispersal

Question 2

what is pollen

Answer 2

a coarse, powdery substance comprising of pollen grains (male microgametophytes) which produce male gametes

Question 3

how do gymnosperms differ from angiosperms

Answer 3

• dont produce flowers
• dont produce true fruit
• no herbaceous forms
• xylems have no vessels
• phloem have no sieve tube elements

Question 4

what is a coniferophyta

Answer 4

a classification of gymnosperm (the conifers) which are the largest and most widespread gymnosperm and dominate many ecosystems

Question 5

what are some characteristics of a pine tree

Answer 5

• evergreen trees with needle leaves
• leaves are produced in bundles of up to 8
• leaves usually live 2-3 years
• leaves have thick cuticles and sunken stomata so it is suitable for growth in areas with low water availability

Question 6

outline the life cycle of a pine tree

Answer 6

1) the tree is a mature sporophyte generation
2) there are seperate male and female cones on the same tree
3) male cones produce pollen grains (microgametophytes)
4) females produce ovules, megagametophytes and seeds
5) seed production can take up to 3 years from pollination

Question 7

where are male cones usually found in pine trees

Answer 7

found in clusters and the lower part of the tree

Question 8

outline the structure of a male pine cone and its gametophytes

Answer 8

• simple with central axis with microsporophyll’s which bear microsporangia
• microspore mother cells undergo meiosis to produce 4 haploid microspores
• each microspore develops into a microgametophyte (pollen grain) of 4 cells
• pollen grains have two air bladders, tube cell and generative cells

Question 8

outline the structure of a male pine cone and its gametophytes

Answer 8

• simple with central axis with microsporophyll’s which bear microsporangia
• microspore mother cells undergo meiosis to produce 4 haploid microspores
• each microspore develops into a microgametophyte (pollen grain) of 4 cells
• pollen grains have two air bladders, tube cell and generative cells

Question 9

what has happened to the antheridia in many gymnosperms

Answer 9

it has been reduced to a single generative cell within the pollen grain which divides and gives rise to 2 sperm cells

Question 10

outline the life cycle of female cone gametophytes

Answer 10

1) megasporangium contains megaspore mothers cells which divides by meiosis to produce 4 haploid megapsores
2) only 1/4 megaspores survives
3) free nuclear division inside the megaspore fives rise to the coenocytic cell which eventually forms the megagametophyte

Question 11

where are megasporangium found in the female pine cone

Answer 11

the ovuliferous scale

Question 12

what odes the megagametophyte contain

Answer 12

1) 3 archegonia each with a single haploid egg

Question 13

outline the structure of a female cone

Answer 13

the ovule is enveloped in an integument which has an opening called the micropyle at its apex which allows the entry of pollen

Question 14

outline pollination in pine cones

Answer 14

1) in spring pollen grains are released from male cones and carried by the wind to female cones
at this point the female cone is small and it its first year

1) a pollination drop exudes from the micropyle of the ovule
2) pollen is drawn in towards the nucelluls as this evaporates
3) the pollen germinates to produce a pollination tube from the tube cell
4) pollen tube grows through the nucellus to the egg in the archegonia

Question 15

outline fertilisation in pine cones

Answer 15

1) the genrative cell in the pollen divides produced two sperm cells
2) both sperm are released into the archegonia but only one fuses with the egg cell to produce a diploid zygote
3) each egg in each of the three archegonia may be fertilized but usually only one zygote developes into an embryo

Question 16

outline the structure of a seed

Answer 16

each ovule on the ovuliferous scale of the female cone develops into a seed protected by a seed coat developed from diploid integuments
- the diploid embryo is within the seed
- the seed is embedded in the haploid megagemetophyte tissue

Question 17

what does the embryo of a pine tree consist of

Answer 17

1) hypocotyl-root axis
2) apical meristem
3) cotyledons
4) root cap

Question 18

what is a cycada

Answer 18

another classification of a gymnosperm found in the tropics and subtropics

Question 19

outline the characteristics of a cycada

Answer 19

• dioecious
• females produce very large cones
• male produce pollen and motile sperm
• beeteles often involved in pollination
• many contain neurotoxins

Question 20

what is a gingko

Answer 20

a classification of gymnosperm whihc only has one representative (maidenhair tree) which has survived in the temple gardens and holy places in china and japan

Question 21

what are gnetophyta

Answer 21

an odd mixture of gymnsperms comprising of 3 living genera and are the closest living ancestors to angiosperms