Lecture 13: Gymnosperms and Angiosperms Flashcards
Gymnosperms
seed-forming, non- flowering plants (pines, cycads, etc.)
Development of pollen and seeds removed _
the requirement for water for reproduction
Pollen
Tiny capsule which contains the male gametophyte and the sperm produced by the gametophyte
* Dispersal by wind (sometimes animals)
Seed
Sporophyte embryo packaged into a hard-shelled capsule with food
* Dispersal by wind (sometimes animals)
Cones
Scaly sporophylls produced by gymnosperms
Gymnosperms produces two types of cones
female and male
Prefixes used to refer to the gender of the cone structures
- ‘Micro-‘ is the male reproductive structures
- ‘Mega-‘ is the female reproductive structures
Male cone
- Male cone are the microsporophylls (2n) which contain the microsporangium (2n)
- Microsporangum (2n) produces microspores (n) via meiosis
- Microspores grow into the male gametophyte (n), and produces the sperm (n)
- Male gametophyte and sperm is packaged into a pollen
Female cone
- Female cone are the megasporophylls (2n) which contain the megasporangium (2n)
- Megasporangium (2n) produces megaspores (n) via meiosis
- Megaspores grow into the female gametophyte (n), and produces the egg (n)
- The megasporangia (2n) and the megaspore (n) is contained in the protective integument.
Ovule
Integument + megasporangium + megaspore
Ovule development into the seed after pollination
- After pollen grain attaches to the ovule (pollination), the pollen tube delivers sperm to the egg to produce the zygote (fertilization).
- The zygote grows into the embryo, which is the ‘baby’ form of the new sporophyte
- Other tissues of the female gametophyte becomes the food supply, packaged into seed
- Integument becomes the seed coat
Moss Life Cycle
Zygote grows into sporophyte (2n)
↓
Sporangia (2n)
↓ ( meiosis )
Spores (n)
↓ ↓
M gametophyte (n) F gametophyte (n)
↓ ↓
Fertilized zygote (2n) (Dispersal by Water)
Gymnosperm Life Cycle
Seeds grow into sporophyte (2n)
↓ ↓
Male cone Female cone
* Contains * Contains
microsporangia (2n) megasporangia (2n)
↓ ↓ (meiosis)
microspores (n) megaspores (n)
↓ ↓
Male gametophyte Female gametophyte
with sperm (n) with egg (n)
* contained in pollen * contained in ovule
↓ ↓
(Pollen dispersal by wind)
Fertilized zygote (2n) grows into embryo, packaged into seeds
Gymnosperm (pines etc.)
- Greek: gymnos-sperma, naked-seed
- Ovule is exposed to the environment
- Upon pollination, ovule develops into seed
Angiosperm (flowering plants)
- Greek: angeion-sperma, container-seed
- Ovule is encased inside the ovary
- Upon pollination, ovule develops into the seed, ovary develops into the fruit
Some gymnosperms produce a fleshy, fruit-like structure. Is this a true fruit?
Not a true ‘fruit’ since it is not derived from an ovary
Angiosperms: Take full advantage of terrestrial environment
- Angiosperms are seed-forming, flower- and fruit-forming plants
- Development of flowers and fruits allowed angiosperm to take full advantage of the terrestrial environment (such as animals)
- Some pollens and seeds (fruits) specialized for dispersal by animals
- Other pollens and seeds (fruits) specialized for more efficient dispersal by wind
Flowers have unique structure to facilitate
pollination via animals
Sepal
base of the flower, encloses the flower before it opens
Petal
brightly coloured portion of the flower to attract pollinators
* Some flowers are wind pollinated
Stamen
male reproductive organ
* Anther contains microsporangia to produce pollens
* Filament is the supportive structure with anther on its end
Carpel
female reproductive organ
* Stigma is the sticky tip of carpel to capture
pollens
* Style connects the stigma to the ovary
* Ovary is the base of carpel that contains the ovules
Ovule
integument + megasporangia + megaspore
Angiosperm ovules are contained in
the ovary
Pollen grain on anther gets dispersed by
animals / wind
Pollen lands on the
stigma of the carpel (pollination)
* Pollen tube grows from the pollen to the ovule to deliver the sperm to egg
As with gymnosperms, the ovule develops
into the seed that contains the embryo
The ovary of the flower develops
into the fruit
Flowers life cycle
- Megasporangium in each ovule produces megaspore. Megaspores grows into female gametophyte which produces egg.
- Microsporangium in the anther produces microspores.
- Microspores develops into male gametophytes, which gets packaged into pollen alongside its sperm. Pollen gets delivered to stigma (pollinization) and pollen tube begins to grow.
- Pollen tube reaches the ovary and delivers sperm to the ovule.
- Fertilization of egg and sperm into zygote.
- Zygote develops into the embryo. Other parts of ovule develops into the seed. The ovary develops into the fruit.
- Seed gets dispersed and grows into the ‘mature plant’ (sporophyte).
Flower diversity
- This diversity is the result of angiosperms taking advantage of the various creatures on terrestrial land to facilitate pollination
- …aside from those which were bred by humans specifically for their shape and colour
Fruits develop from __ to (usually) __
ovaries
encase the seed
* Protects the seeds and help with dispersal
Fruits can be
fleshy or dry
* Fleshy fruits: tomatoes, plums, grapes, etc.
* Dry fruits: beans, nuts, grains of rice, etc.
Fruits facilitate dispersal of seeds, with the most common methods being
Dispersal by animals
Dispersal by wind
Dispersal by animals
- Some fruits gets dispersed by animals
- Eaten by animals, and the undigested seed gets released with the feces
- Stored underground by animals (and gets forgotten)
- Sticks on to animals to get carried around
Dispersal by wind
- Some fruits are specialized for wind dispersal
- For example, dandelion fruit and the maple fruit which have a wing-like structure to glide in wind
Different types of fruits
- Simple fruit
- Aggregate fruit
- Multiple fruit
- Accessory fruit
Simple fruit
*Derived from a single carpel or several fused carpels
Aggregate fruit
- Derived from a single flower with a group of individual carpels each forming a small fruitlet
- Fruitlets become clustered together
Multiple fruit
- Derived from group of flowers clustered together
- Ovaries mature and fuse together into ‘one’ fruit
Accessory fruit
- Other parts of flower develops into what humans perceive as the ‘fruit’
Apple is an accessory fruit
- The ‘core’ of the apple is its actual fruit, developed from the ovule
- Majority of the fleshy, edible portion is derived from the receptacle tissue which surrounds the ovule
Dandelions produce
multiple, clustered fruits from multiple, clustered flowers
Dandelion fruit is specialized for
wind dispersal, floating in air
* The white wings are called pappus
Is the Dandelion flower a single flower?
- The dandelion ‘flower’ is not a single flower
- It is many small florets clustered together
- Each seed-head contains about 40–100 florets
ROOTS
- Anchors vascular plant in soil and absorbs mineral and water
- Often stores carbohydrates and other reserves for the plant to use
- Carrots stores food directly in their roots (root veggies)
- Potatoes are tubers, which store food in specialized structures which developed from parts of their root
Roots and the nitrogen cycle
- Plants use roots to absorb nitrogenous compounds in soil
- Nitrate (NO3-) is what’s mainly absorbed via the root, plus some ammonium (NH4+)
- Soil-living, nitrogen fixing bacteria fix nitrogen gas in the atmosphere (N2) to ammonia (NH3)
- Ammonia gets converted to ammonium in soil
- Some of these nitrogen fixing bacteria are
free living - Others form a symbiotic relationship with certain types of plants
Nitrogen cycle & Rhizobium sp.
- Bacteria of Rhizobium sp. coexist inside specialized root nodules of their host plant
- Growing plant invite Rhizobium sp. to infect their root, while the bacteria also emits chemicals to facilitate the process.
- The infected area develops into nodules for Rhizobium to live inside.
- A vascular system is established between the nodule and root for nutrient exchange.
Why is Rhizobium sp. necessary in context of the nitrogen cycle
- Nodule provides an anaerobic environment for Rhizobium to fix nitrogen
- Plant also provides other nutrients to keep Rhizobia population healthy
- Rhizobium provides the plant with fixed nitrogen
- Many species of legume plants can form this mutualistic relationship
- Beans, lentils, chickpeas, alfalfa, clover
Crop rotation
- Many commercially important crops such as wheat absorb nitrogen from soil
- Growing the same crop in the same field over many years in a row depletes essential nutrients (monocropping)
- Other crops such as legumes can add nitrogen to soil via their mutualistic nitrogen- fixing bacteria
Crop rotation definition
Plant nitrogen-absorbing crops and legumes in a rotation to help sustain the nutrient content of the field
Three field system
- First field: Nitrogen-depleting crops such as wheat/rye
- Second field: Legumes such as peas and beans
- Third field: No crop planted. The field gets overgrown by weeds. Animals are grazed on this land to add more nutrients via their feces.
Why is the Three Field System useful
- Crop rotation drastically increases the amount of crop yield while reducing the need for artificial fertilizers
- Crop rotation was a key innovation for human society to sustain a high population
