Lecture 13 Flashcards
Gymnosperms are
Seed-forming, non-flowering plants
Development of pollen and seeds in gymnosperms removed
the requirement of water for reproduction
Pollen
Tiny capsule which contains the male gametophyte and the sperm produced by the gametophyte - dispersal by wind and sometimes animals
Seed
Sporophyte embryo packaged into a hard shelled capsule with food - dispersal by wind and sometimes animals
Cones
Scaly sporophylls produced by gymnosperms
Two types of cones are produced: Female and male
Prefixes used to refer to the gender of cones
Micro: Male reproductive structures
Mega: Female reproductive structures
Male cones
Contain the microsporophylls (2n) which contain the microsporangium (2n)
Microsporangium (2n) produces
Microspores (n) via meiosis which grow into the male gametophyte (n) and produces the sperm (n)
- Male gametophyte and sperm is packaged into a pollen and dispersed by wind
Female cone are the
Megasporophylls (2n) which contain the megasporangium (2n)
Megasporangium (2n) produces
megaspores (n) via meiosis which grow into the female gametophyte (n) and produces the egg (n)
The megasporangia and the megaspore (n) is contained in the
protective integument
Ovule = Integument + Megasporangium + megaspore
How does the ovule develop into a 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 and integument becomes the seed coat
Gymnosperm has an extremely
Sporophyte dominated life cycle
moss life cycle
Zygote grows into sporophyte -> sporangia (2n) -> Spores (n) -> male and female gametophyte -> fertilized zygote after sperm dispersal
Gymnosperm life cycle
Seeds grow into sporophyte (2n) -> Male and female cones contain micro/mega sporangia -> micro/mega spores (n) -> male (contained in pollen) and female (contained in ovule) gametophytes -> fertilized zygote grows into embryo packaged into seeds after pollen dispersal by wind
Major difference between gymnosperm and angiosperm
Gymnosperm (pines)
- “naked seed”
- Ovule is exposed to the environment
- Upon pollination, ovule develops into seed
Angiosperm (flowering plants)
- “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 but is not a true fruit as it is not derived from an ovary
Juniper berry
- Allows Seed dispersal by animals
- Convergent evolution, acquiring the same function as the fruits produced by angiosperms
Angiosperms are
Seed forming, flower and fruit forming plants
Development of flowers and fruits allowed angiosperms to take full advantage of the terrestrial environment
Some pollen and seeds (fruits) specialized for dispersal by animals but others disperse by wind
How do flowers make animals help pollination
- Unique structure to facilitate pollination via animals
Sepal: Base of the flower, enclosed the flower before it opens
Petal: Brightly coloured portion of the flower to attract pollinators
Flowers and pollination: Stamen and Carpel
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 (contained in ovary) = Integument + megasporangia + megaspore
Pollination and production of seed and fruit
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 the contains the embryo
Ovary of the flower devlops 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
Is the result of angiosperms taking advantage of the various creatures on terrestrial land to facilitate pollination
Fruits
Develop from ovaries to encase the seed
- protects the seeds and help with dispersal
Can be fleshy or dry
flesh fruits: tomatoes
Dry fruits: beans, nuts
Fruit dispersal
Dispersal by animals
- Eaten by animals and the undigested seed gets released with feces
- Stored underground by animals
- Sticks onto animals to get carried around
Dispersal by wind
- Dandelion fruit
Different types of fruits
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 develop 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 (flesh) tissue which surrounds the ovule
Dandelion produces multiple
clustered fruits from multiple clustered flowers
Dandelion fruit is
Specialized for wind dispersal, floating in the air
- White wings are called pappus
- Single dandelion fruit develops from one flower and its ovary
- Single dandelion seedhead develops with many fruits attached to it
The dandelion ‘flower’ is not
a single flower, it is many small florets clustered together
Each seedhead contains about 40-100 florets
Roots
Anchors vascular plant in soil and absorbs mineral and water
Often stores carbohydrates and other reserves for plant to use
Carrots stores food directly in their root (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 such as NO3 nitrate plus ammonium NH4
Soil living nitrogen fixing bacteria fix nitrogen gas in the atmosphere to ammonia
- Some of these nitrogen fixing bacteria are free living whereas others form a symbiotic relationship with certain types of plants
Example of nitrogen fixation with bacteria of Rhizobium sp.
Bacteria coexists inside specialized root nodules where growing plant invites the bacteria 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 then established between the nodule and root for nutrient exchange
The nodule provides an anaerobic environment for rhizobium to fix nitrogen whereas the plant also provides other nutrients to keep bacteria population healthy
Examples of legume plants that can form a mutalistic relationship between nitrogen fixing bacteria
Beans, lentils, chickpeas
Crop rotation
Many commercially important crops such as wheat absorb nitrogen from soil
Growing the same crop in the same field over time depletes essential nutrients
Other crops such as legumes can add nitrogen to soil via their mutualistic nitrogen fixing bacteria
Crop rotation: Plant nitrogen-absorbing crops and legumes in a rotation to help sustain the nutrient content of the field
Three field crop rotation
First field: Nitrogen depleting crops such as wheat
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
Crop rotation drastically increases the amount of crop yield while reducing the need for artificial fertilizers
