Transport and Reproduction in Angiosperms

Topics 9.2-9.3

Water and mineral uptake·Occurs in the roots which have adapted in several ways for this process:

> Roots are covered in tiny hairs that increase the surface area (by nearly 3X) for greater water absorption

> Branching allows the roots to cover a greater area and thus increase mineral and water uptake

> Cortex cell walls are permeable and therefore allow for osmosis

Water uptake·Must pass through several regions of root before it enters the vascular cylinder:

epidermis --> cortex --> vascular cylinder·Water enters root hairs because they have a higher solute concentration and a lower water concentration than the surrounding soil.

>moves through plasma membranes into root hair cells

·Once in the root, water moves to vascular cylinder by

> Symplastic route: moves from cell to cell> Apoplastic route: moves through cell walls and the extracellular spaces

Mineral ion uptake ·Ways in which minerals can move to roots

1. Diffusion of mineral ions and mass flow of water in the soil to the root

2. Mutualistic relationships with fungal hyphae

> Plant root provides fungi with nitrates in exchange for needed minerals

3. Active transport

Mineral ions are taken in to the plant by active transport1. Integral membrane proteins transport

minerals from the soil in to the root2. Once the minerals have crossed over into

the plants they attract water through a concentration gradient

II. Water has multiple functions for terrestrial plants1. Transpiration = loss of water vapor from the leaves and stems

of plantsa. Xylem cells are dead and therefore have no

cytoplasmb. The empty space left allows for passage of water

moleculesc. Due to their polar nature, water molecules bond to

the xylem walls (adhesion) as well as each other (cohesion), thus forming a chain in the xylem

d. When light hits the leaf it’s temperature increases and water in the spongy mesophyll vaporizes (evaporation)

e. When one water molecule is lost from the stomata of a leaf due to evaporation, the chain of water molecules

that proceed it are pulled upwards

g. Stomata can control the amount of water lost to transpiration by opening and closing

i. This is controlled by guard cells that surround the stomata-If the solution inside of the guard

cells is hypotonic to the surrounding

solution water will rush in osmotically and cause the guard cells to swell, thus opening the stomata

- If the surrounding solution is hypertonic, water will leave the

guard cells which will then shrink and allow the stomata to close

ii. under normal conditions the stomata remain open during the day to allow for CO2 uptake and are closed at night when no photosynthesis is taking place

iii. If the plant becomes dehydrated during the day (e.g. hotter than normal temps) the mesophyll cells will release abscisic acid

iv. abscisic acid will cause the stomata to close in order to prevent more water loss

h. Many abiotic factors affect the rate of transpiration

i. Light affects blue light receptors in the leaves that open stomata by creating a

potassium gradient (potassium is pumped into the guard cells and water follows due to osmosis)

ii. Hot temperatures cause stomata to close (transpiration rate decreases)

iii. Wind causes air near the leaves to be very dry and thus increases the rate of

transpirationiv. Humidity causes the air near the leaf to

be more moist and therefore decreases the rate of transpiration

III. Transport of food/nutrientsA. Phloem is a living tissue that transports food (sucrose, amino

acids, other nutrients) from leaves where it is made (via photosynthesis) to the roots or fruit

B. This is called “from source to sink”C. The phloem is composed of “sieve tube cells” which lack a

nucleus, have very few vacuoles, but have other organelles such as ribosomes

D. Sieve-tube cells are surrounded by companion cells that help to transport sucrose into the phloem from surrounding tissue at the source and out of the phloem to surrounding tissue at the sink

E. Active transport fueled by ATP pumps sucrose molecules into the phloem cells

F. Water then follows the sucrose (osmosis) and the resulting pressure causes the sap (sucrose solution) to move through the phloem

G. The process is reversed at the sinkH. If the sink is a root, the sugar will be stored as starch. I.

Examples include carrots (thick roots) and potatoes (tubers)

Reproduction in Angiospermophytes

Topic 9.3

Flower Structure:

I. Reproduction in Flowering Plants (angiospermophytes)A. Flowers 1. Flowers are reproductive shoots composed of four main parts: sepals, petals, stamens (composed of the filament and anther), and carpels (composed of the style and stigma)2. All four floral parts are important in the reproductive process, but only stamens (the “male” organs) and carpels (the “female” organs) produce gametes3. A flower that has all four parts is said to be “complete” whereas one that does not have all four parts is “incomplete”4. A flower with both stamens and carpels is said to be “perfect” whereas an “imperfect” flower has one or the other but not both

Function of flower structures:·Sepals cover and protect other flower parts when the flower is a bud·Petals play an important role in attracting animal pollinators to the flower

·Stamens are composed of a stalk called the filament and a saclike anther where meiosis occurs to form pollen grains

> Each pollen grain produces two cells surrounded by a tough outer wall

> One cell eventually divides to form two male gametes, or sperm cells, and the other produces a pollen tube through which the sperm cells travel to reach the ovule

·Carpels (AKA pistil) bear ovules, which are the structures with the potential to develop into seeds

> may be separate or fused into one structure> 3 sections:

-stigma (where the pollen grain lands) - style (a neck like structure through

which the pollen tube grows)- ovary (an enlarged structure that contains one or more ovules)

- Each young ovule contains a female gametophyte that forms one female gamete

(an egg), two polar nuclei, and several other haploid cells- Following fertilization, the ovule develops

into a seed and the ovary into a fruit

Pollination, Fertilization, Seed Dispersal·Pollination refers to the placement of pollen onto the stigma of a carpal/pistil by wind or animal carriers; a pre-requisite to fertilization.

·Fertilization refers to the union of haploid gametes (pollen and egg) to produce a diploid zygote

> occurs within the ovary of a plant> The zygote is now the seed

·Following pollination and fertilization is seed dispersal, which describes the action of the seed moving from its place of origin to another site where it will grow

Seed structure1. Cotyledon = embryonic leaf and food storage2. Radicle = embryonic root3. Plumule = embryonic shoot4. Testa (Seed coat) = protects the seed5. Micropyle = takes in water for germination, site

radicle grows out of

Requirements for Germination·Each type of seed needs its own optimal combination of:

> Oxygen for aerobic respiration> Water for metabolic processes in cells> Temperature for function of enzymes

·Some species have other requirements to match germination to favorable conditions:

> fire > freezing > photo period> passing through digestive system of animal> erosion of seed coat

Metabolism in Seed Germination1. Water causes gibberellin to form in the

cotyledon2. Gibberellin stimulates the production of amylase,

which catalyses the breakdown of starch to maltose (from the cotyledon)

3. The maltose diffuses to the embryo for energy production and growth

Control of Flowering·Flowering cues

> Plants have to coordinate the production of flowers to coincide with the best reproductive opportunities

> There are many environmental cues that affect flowering however the photoperiod is the most reliable indicator on 'time' of year.

> The photoperiod the period of day light in relation to dark (night). > In northern and southern regions this photoperiod is a reliable indication of the time of year and therefore one of the most reliable indicators of the seasonal changes.

Short and Long Day Plants·Short day plants (SDP) typically flower in the spring or autumn when the length of the day is short·Long day plants (LDP) typically flower during the summer when the photoperiod is longest

Critical Night Length·Studies have shown that it is the length of night that is critical to when flowering occurs·SDP have a critical long night (length of night must exceed a certain length for flowering to occur)·LDP have a critical short night (length of night must be shorter than a certain amount for flowering to occur)

Phytochrome System·The receptor for photoperiod is located in the leaf·'Phytochrome' is the chemical involved

> Has two forms that can be converted from one form to another by wavelength of light

- Phytochrome red (Pr) - more stable, inactive- Phytochrome far red (Pfr) - less stable, active

* white/red light converts Pr to Pfr

* far red light converts Pfr to Pr

> Day light contains more white/red light than far red light, so during daylight hours the concentration of Pfr increases.

> In the dark, Pfr is slowly converted back to the more stable Pr

Flowering in SDP·Short day plants flower when the night period is long. ·A long night means that there is a long time for the conversion of Pfr back to Pr

·Under short day conditions (long night) at the end of the night period the concentration of Pfr is low.·In SDP, Pfr inhibits flowering, a low Pfr concentration is the trigger for flowering.

Flowering in LDP·Long day plants flower when the night period is short.·During periods when the day light period is long but the dark period is short, Pfr does not have long to convert back to Pr so a higher concentration of Pfr remains.·In LDP, Pfr promotes flowering, a high Pfr concentration is the trigger for flowering.