Gymnosperms

Question 2

what helps spore dispersal

Answer 2

• To help the spores spread as far as possible, the sporangia should be raised as high as possible
• for mosses which are very short, the sporophyte is always the highest point (on top of the gametophyte)
• In ferns, the sporophyte is independent of the gametophyte, and can even be a tree. Which can produce billions of spores.

Question 3

what are the trade off of small spores

Answer 3

• small spores (like what ferns use) can travel farther and occupy distant lands, and it is possible to make more of them
• the disadvantage of small size, means low investment, dooming new plants to a slow start

Question 4

why did some ferns make the female gamete bigger

Answer 4

• But some ferns changed their strategy, doing what many eukaryotes tend to, and invest more in the gender that takes care of the zygote
• In these heterosporous ferns, the female (or megagametophyte) is bigger, since it is carrying the next generation’s food.
• This nutrient loading is happening on the sporophyte, which is indirectly providing the next sporophyte with a head start by directly investing in the gametophyte.

Question 5

what happens to the male gamete in the ferns with giant female gametes

Answer 5

• the male gametophyte became tiny, and the microgametophyte forms from cell division within the spore wall
• Microgametophytes can be blow thousands of miles
• and Megagametophytes just drop from the tree and don’t get around much
• having lots of microgametes ensures a higher chance of mating

Question 6

what does a zygote need to be successful

Answer 6

• considering the young plant that develops from the zygote
• To become independent, the young plant must build infrastructure, namely
  
  • a sufficient photosynthetic surface to produce nutrient
  • an anchoring system to support its new “solar panels” and supply them with water for coolant and reactants.
• The gametophyte’s energy-rich reserves (such as the 3 main macros) give the sporophyte a head start in building infrastructure like (roots, leaves, shoots)
• Heterosporous plants can grow to 30+ m tall and dominated early landscapes like lycopophyte Lepidodendron in the Carboniferous

Question 7

what are the 4 phyla of gymnosperms

Answer 7

4 phyla:

1. Cycadophyta
2. Coniferophyta
3. Gingkophyta
4. Gnetophyta

Question 8

how did gymnosperms change the megagametophyte

Answer 8

The Sporophyte held on to the magagemtophyte eventually enclosing it. The new hybrid structure - part megagametophyte, part sporophyte is called an ovule.

Question 9

what are the benefits and costs of a ovule

Answer 9

Benefits:

• Longer loading of nutrients and greater accumulation of storage reserves
• Sporophyte defends the gametophyte

Costs:

• More attractive to predators
• Cost borne by sporophyte

Question 10

what does the sporophyte do to the microgametophytes before fertilization in gymnosperms

Answer 10

1. The sporophyte provided liquid (pollination drop) to capture microgametophytes
2. The sporophyte ovule used one of its own tissues (nucellus) to screen microgametophytes

Question 11

what change did gymnosperms make to the megagametophyte

Answer 11

The megagametophyte stopped photosynthesizing ever again. We have one generation of plants, the gametophyte, that no longer is green. Instead it converted sugars and amino acids supplied by the sporophyte into starches, protein bodies, and fat bodies.

Question 12

how did gymnosperms change gamete size

Answer 12

4. Gamete size changedThe megagametophyte increased the size of its eggsthe sporophyte is investing in the future of the embryoSperm changes:
   1. it goes gigantic in cycads
   2. it becomes flagellae-free in conifers
   the microgametophyte is now formed entirely within the microsporeit germinates to produce a pollen tube to deliver the gametes into the ovuleIt is now known as pollen.Ancient but living gymnosperms like cycads have flagellated sperm. A single cycad sperm is so large (400um in diameter) that it can be view by the human eye without any magnification. Each sperm has 20,000 flagella

Question 13

how do gymnosperms pollinate

Answer 13

Now that megagametophytes are no longer in puddles on the ground, but held high in the air by the sporophye how does pollination happen, and do plants still use the rain?

Gymnosperms use two methods to get their pollen to the ovule

1. wind
2. insects

Question 14

what are seeds and their advantages

Answer 14

a seed is a fertilized ovule

what are the advantages of seeds:

1. they can go dormant, so can delay growing till conditions are optimal (like protist cysts)
2. they can be transported long distances by wind or animals, which means dispersal is optimized.

Question 15

how does wind pollination work

Answer 15

In most gymnosperms the male cones release pollen which is carried in large clouds by the wind.

The pollen blows into cones where the ovules are stacked in pairs on scales.

Question 16

what is a pollination drop and what does it do

Answer 16

The ovule has an opening called a micropyle. Where a pollination drop appears at the opening and billows out like a sphere.
The pollination drop catches the pollen. The drop recedes into the ovule while carrying the pollen. The Ovule then shuts.

Using pollen drops, Gymnosperms don’t rely on rain for reproduction.

Question 17

what does a pollination drop contain

Answer 17

• Calcium: helps pollen germinate
• Sugars: provide energy to germinated pollen
• Amino acids: provide energy to germinated pollen
• Proteins: Kill bacteria, fungi, and viruses that enter the ovule (safe sex)

Question 18

what does the nucellus do

Answer 18

the nucellus is the equivalent of the megasporangium. It:

• Performs Meiosis
• and makes the pollination drop

Question 19

what makes up a seed

Answer 19

Outside:

1. Seed coat (equivalent or Integument) 2n

Inside:

1. Megagametophyte n
2. Embryo 2n

Seed coat has genotype of material

Embryo has mixed genotype

Question 20

what groups of gymnosperms are insect pollinated

Answer 20

there are 4 groups of living gymnosperms, of them: 2 are insect pollinated

• Cycadephyla
• Gnetophyta

Question 21

explain Push-Pull-Thermogenic Insect Pollination

Answer 21

-In australia, cycads of the genus Macrozamia are pollinated by and ancient insect group called thrips.

They have a weird pollination syndrop called:

Push-Pull-Thermogenic Insect Pollination

Here’s how it works:

• in the morning insects enter the male cones where they feed on the pollen (a reward)
• At noon there is a thermogenesis event, a 15º rise in the internal temperature of the male cones because of the unpleasant heat and an unpleasant scent the cones release the thrips leave the male cones (this is the push part)
• By mid afternoon, the cones cool to ambient temperature, but but by then the thrips have left.
• Female cones omit an odour that attracts the thrips to them, they enter the female cones (where they reproduce with other thrips) (this is the pull part)
• As the thrips enter, covered in pollen, they brush past ovules, and leave some pollen in the pollination drops.

Question 22

describe the lifecycle of male lodgepole pine

Answer 22

Year 1: Tree grows and produces male cones

Year 2: meiosis occurs in the cone, resulting in microspores, which are dispersed by wind or insects, and pollinate by entering the ovule

Year 3: fertilization occurs

Question 23

explain the lifecycle of female lodgepole pine

Answer 23

• Year 1: tree develops female cones
• Year 2: meiosis occurs in the cones resulting in 4 megaspores, where only 1 survives, pollination occurs when pollen from the male tree enters the ovule
• Year 3: the megagametophyte forms, and the seed is produced

Question 24

describe an overview of lodgepole pine reproduction

Answer 24

• It takes 13 months from pollination to Fertilization
• Delayed fertilization is a hallmark of gymnosperms

The making of a gymnosperm seed is slow:

• year 1: initiation of male and female cones
• year 2: female cones open and receive pollen from moles
• year 3: pollen fertilizes megagemetophytes, the embryo develops within the seed.