Lecture 21 - Gymnosperms

examples of gymnosperms

pine trees, firs, larches, junipers/cedars, redwood trees, bald cypress trees, and yew trees

redwood tree variations

Sequoia sempervirens and Sequoiadendron giganteum

yew tree reproductive structures

resemble fruits (berries) but are not fruits; derived from cone structures

gymnosperm evolutionary characteristics

share same characteristics as SLVPs, but don’t need water for fertilization and have seeds (LACK FRUITS)

only in Angiosperms

fruit

the seed coat

encloses embryo and nutritive tissues

endosperm

nutritive tissues

is the seed a GP or a SP

SP (all land plants are SP)

what material is the SP embryo embedded in?

In SLVPs, embryo is connected via placenta tissue to GP; while there is no placenta tissue in a mature seed, tissue surrounding the SP embryo is gametophyte tissue

how is the embryo formed?

if the embryo is SP, it is formed by fusion of gametes (fertilization) while results in a gamete.

where are gametes formed?

In SLVPs, archegonia and antheridia of GPs;

In seed plants, GP is extremely reduced.

Is GP bisexual?

all seed plants are heterosproous (can be either male or female)

gymnosperm seed anatomy

seeds grow on the surface of a scale in a cone (ex. pine cone)

ovuliferous scales

seed-bearing scales; seed develops from an ovule

“gymnosperm”

“naked seed,” sit uncovered on the scale of a cone

pinus

female cone

seed

a mature ovule containing an embryo; embryo + stored food (GP) + seed coat

what does a seed consist of?

embryo embedded in nutritive endosperm tissue, which is encapsulated by the seed coat.

in simple terms…an embryo together with stored food packaged in a seed coat

what is the endosperm derived from?

gametophytic tissue

seed coat advantages

able to withstand adverse environmental conditions and represents a dormancy state

what is a seed derived from?

ovule; ovule develops into a seed

ovule (PART OF SP)

An immature ovule before meiosis consists of nucellus (= megasporangium) + megaspore mother cell + integuments.

seed plant life cycle

sporic meiosis

meiosis in ovule

formation of spores and gametophytes

integuments

develop into the seed coat

megaspore mother cell

produces a spore that will produce the megagametophyte (“mother” of the megaspore); diploid cell that will undergo meiosis to form four spores of which one is the ‘megaspore’

ovule AFTER meiosis

nucellus, gametophyte, and integuments

ALL spores

haploid and formed by meiosis

what about the other 3 spores?

They will disintegrate leaving only the megaspore behind.

megaspore

megaspore of gymnosperms will develop into the (mega-) gametophyte

how is reproduction different in SLVPs?

the (mega-)sporangium contains 'sporogenous tissue' with
multiple cells that undergo meiosis and produce multiple spores.

GYMNOSPERMS ONLY HAVE ONE CELL THAT UNDERGO MEIOSIS

spores in SLVPs

dispersal unit, released after meiosis

spores in gymnosperms

megaspore never leaves the megasporangium

advantages of seeds

fertilization independent of water, increases survival, can serve as dormancy state, growth of embryo is supported by food reserves stored in seed, dispersal using wind and animals is more effective than spores.

male GP in seed plants

transferred bodily to the female GP where it grows a pollen tube to bring the immotile sperm to the egg cell