BC: AP Biology Period 1 Lab Table 6
FC: Our Baby Plants | Baby Plants | Karen Altergott, Julia Carlson, Emma Fisher, Georgia Schneider, and Linnea Wethekam | Proudly presenting our little baby radish... Leaf Erikson!
1: Leaf Erikson January - March 2013
2: The very beginning... | On January 31, 2013, 38 absolutely adorable seeds were planted in 5 very lucky pots...
3: Cute as a button | Then they were placed in a lovely environmental chamber to germinate and grow.
4: Seed Structure & Function | EMBRYO: The embryo is a small structure within the seed. It is nourished by the endosperm and protected by the seed coat so that, when conditions are right, it can germinate and eventually grow into a strong plant... like our little Leafie. The embryo is composed of the radicle (seed root), the hypocotyl (seed stem), and many meristem cells. Together, these structures make up the developing organism. In seeds, the embryo is dormant until imbibition which initiates germination. | Detailed diagram of embryo parts | NOTE: The stored food (endosperm) of a dicot (like the radish seed) is stored within its cotyledons | NOTE: The stored food (endosperm) of a dicot (like the radish seed) is stored within its cotyledons
5: Baby Girl | COTYLEDONS: Cotyledons store food and nutrients for the seed, and also serve as the developing plant's first leaves. They are needed to harvest sunlight and perform photosynthesis to nourish the plant between the time when the seed's main food stores (especially in the endosperm) can no longer sustain the plant, but before true leaves have grown. Monocots have one cotyledon; dicots (like Leaf Erikson the radish plant) have two. They surround the embryo. | ENDOSPERM: The endosperm is a triploid tissue found in angiosperm seeds. It surrounds the embryo and fills the space within the seed coat that is not taken up by the embryo or coyledons. It is generally rich in lipids, starches and proteins necessary to sustain the embryo before it germinates, grows leaves, and is able to photosynthesize its own food.
6: By day 4, stems had grown...
7: GERMINATION: After fertilization an embryo remains in a non-growing state within its seed. When the seed resumes its growth to form a seedling, germination occurs. External factors that influence germination include the temperature, abundance of water and oxygen, and the amount of light or darkness that a seed is exposed to.
8: 'Seeds need to take in water in order to swell and break the seed coat so roots and leaves can begin to grow. A huge influx of water, called imbibition, is therefore the first step in germination. Until a seed grows leaves, it is dependent on oxygen in the soil as the source of oxygen for aerobic respiration that provides energy for the seed. Seeds often have a temperature range that they can germinate within, if the temperature isn't favorable then the seed won't germinate. | In certain environments the seed needs to ensure that it will have enough light before it begins germination. Red light promotes germination while far-red light inhibits it. That is because far-red light indicates shade. Within the seed, if there is a large amount of abscisic acid, the hormone will inhibit germination; the hormone gibberellin in large amounts will induce germination.
9: Growing up so fast - by day 8, they were between 4 and 6.5 cm tall, and had cotyledon leaves of approximately 1.5 x 2.3cm. Wow. | Look at those leaves, it even has a cuticle, how adorable...
10: Our Babies at about three weeks
11: Pictures | Plant growth comes from meristems, and there are three types. The apical meristem causes upward growth. Leaf has his apical meristem at the center of junction made between the leaf pairs. Without the apical meristem, the lateral meristem will take over and produce a plant which is shorter and bushier. The final type of meristem is the root meristem, this meristem extends the length and size of the roots, seen in the comparison picture. Primary growth occurs when the meristems are in action, and allow for vertical growth. The meristems are on the tip of the stem, and the bottom of the roots, and at the base of a petiole. Baby Leaf's primary growth was quite amazing, he grew to about 23 cm and even flowered. Secondary growth was not present with our little Leafie, but it does occur in woody plants. Secondary growth is the outward growth. This occurs in the cambium, as new xylem and phloem grow each year the plant grows outward.
12: Plants like humans possess molecules to induce or suppress behaviors. Auxin is the one of the molecules that has the greatest impact across the plant body. Auxin plays a role in many plant processes. Created at the tip of the plant, it causes phototropism and apical dominance. It also promotes the production of ethylene gas, develops adventitious roots, and secondary growth, as well as promoting formation of xylem and phloem. Apical dominance is important to plant growth. The presence of Auxin at the tip of the shoot prevents the lateral buds from growing and ceasing when the apical bud is removed, and causing outward growth. In Leaf we saw another part of Auxins control, in the phototropic response by our plants. One plant had a slight bend in the stem due to the high concentration of Auxin in the shaded part of the stem.
13: Leaf and his siblings were so cute; here is their first haircut! | Gibberellins are hormones that affect stem growth (cell division and growth), and germination, and flowering. The stem of Leaf became quite long and that was due to Gibberellins. Our plants went from seeds to plants because of the Gibberellins. Gibberellins induce the production of a-amylase which breaks down the endosperm to give the embryo energy and resources to grow. The flower that Leafie grew, was also due to the action of Gibberellins, because they promote flowering in plants.
14: Water Transport (because our babies get thirsty) | Primary root | root hairs (better not get a hair cut)
15: Water moves through a plant by means of the dead transportation tissue, xylem, which is composed of tracheids and vessel elements. The process of cohesion-tension is carried out by the evaporation of water on the leaf surface and the pressure the roots experience. Evaporation occurs when the stomata are open on leaf surfaces; stomata are the openings created by the expansion of guard cells and close due to a loss in turgor pressure in these cells. As water evaporates, the surface tension of the water left becomes greater and pulls water up through the leaves. Cohesion between water molecules causes water from within the xylem tissues to be pulled up. Since the leaves have a decreased pressure potential at their surface and thus have a lower water potential, the roots have a higher pressure potential as water is pulled through the xylem and absorbed by the roots. Water moves from areas of high to low potential, so this gradient is another driving force to send water up the xylem.
16: The process of moving sugars throughout a plant is known as the process of translocation. Sugars are transported through the phloem, which is made of sieve-tube members and companion cells that occur in bundles. The way that translocation is carried out is explained by the pressure-flow hypothesis. Sugar moves from cells where photosynthesis occurs, or sources, to storage cells, or sinks. Phloem is directly next to the xylem, so water is able to enter the phloem. Water enters near sources because there is a higher concentration of sugars, which are pulped out of the source cell that occurs with the cotransport of hydrogen ions, present in that section of phloem. As more water enters, the turgor pressure becomes greater and the water and sugar move from an area of high to low pressure. In this way, sugars are transported to the sink cells and this process is labeled as bulk flow. Sugars can move from root to tip or from tip to root depending on which cells in the plant are sources.
17: Our little sweetie pie | Sugar Transport (because plants need to eat too)
18: Sporophytes make haploid spores through meiosis. | Life Cycle of Our Dear Leaf | Biology sure is interesting
19: During the life of a plant such as our little Leaf, time is spent in two different life-forms: sporophyte and gametophyte. Since Leaf is an angiosperm (look at those lovely flowers), most of his time is spent in the diploid sporocyte phase. The production of pollen grains and a female gametophyte constitute Leaf's entire gametophyte stage. | Gametophytes make haploid gametes through mitosis.
20: DICOTS (like Leaf Erikson) versus MONOCOTS (his extended relatives): Being a radish, our cute little baby Leaf Erikson is a dicot plant. This means it shares a common ancestor with other dicots such as roses, magnolias, grapes, peanuts, oak trees, lentils, beans, and peas. I guess this makes them cousins! They should all be proud of their cute new baby cousin Leaf! As distinct from monocots which have one (“mono”) cotyledon, dicots have two (“di”). When dicots germinate, these cotyledons break through the soil facing downward, below a bend in the embryonic stem known as the hypocotyl arch. On the other hand, monocots break through the soil erect. The tip is covered by a modified leaf structure called a coleoptile, to protect the apical meristem.
21: Aww... Look at little Leaf Erikson's branching veins. What a good looking dicot he is. | Another difference is that monocots like corn, tulips, lilies, and grasses have vascular tissue scattered randomly throughout the stem. Dicots like our wee little Leafie here are much more organized: their vascular tissue is arranged in a ring formation. In leaves, monocot vascular tissue forms parallel veins whereas it has a branching formation in dicot leaves. Additionally, dicots have fibrous roots; monocots have taproots, Another difference between monocots and dicots is found in their flowers. Monocots have petals arranged in sets of three; dicots have petals in sets of 4 or 5. In Leaf's teenage years, that baby had some mighty fine petals:! Look at that classic set of 4 petals. What a true dicot... We're so proud of you Leaf. | Look, Little Leafie's node's | Here's his internode
22: Our babies in the beginning | Her First FLower | He's even budding..
23: Their first Leaves