Topics in Depth
The Theme of Common Mistakes in Plant Biology
Alternation of Generations
Spores and sporophytes vs gametes and gametophytes: all these concepts can be confusing. Luckily, we at Shmoop have vast stores of wisdom to aid our dear readers. Two things to remember:
1. The words ending in "phyte" are plants.
2. The reproductive units plants make can be found at the beginning of the word.
Rather than trying to remember that spores grow into gametophytes and gametes fuse and grow into sporophytes, remember that sporophytes make spores and gametophytes make gametes. Since you know the life cycle is a cycle, and what goes around comes around, it follows that spores grow into gametophytes. Spores can’t grow into sporophytes because that’s where they came from.
Primary and Secondary Growth
Shoots vs. roots:
Shoots are the aboveground parts of the plant (except for rhizomes) and are made up of stems and leaves. Flowers and fruits are also part of the shoot system.
Roots are the defined as the part of the plant that take in water and nutrients and supporting the plant. They are usually belowground, though they don’t have to be belowground. Notable aboveground roots are found in mangroves and epiphytic orchids.
- An apical meristem is an area where new extension growth originates, and both the root and shoot systems have apical meristems.
- There can be more than one shoot apical meristem per plant. In fact, there are as many shoot apical meristems as there are stems and branches. The same is true of root apical meristems.
- A lateral meristem is where new growth originates that adds to the plant’s width, also known as secondary growth.
Secondary xylem and secondary phloem:
Secondary xylem forms on the inside of the vascular cambium, so as the plant gets wider, the vascular cambium gets further and further away from the center of the plant. Secondary phloem forms on the outside of the vascular cambium, but can eventually be sloughed off.
Ground tissue doesn’t have to be in the ground; it is just the name for tissues that are not vascular or dermal.
All the cell types ending in –chyma can be daunting, but there are only three of them. Parenchyma is the most common and the most versatile; collenchyma and sclerenchyma are mostly used in support.
Transportaion in the Plant
Water moves from high concentrations to lower concentrations. But what does it mean for water to be in a high concentration? That means there is a lot of water compared to other molecules, such as solutes that may be dissolved in the water. When you eat a lot of salty potato chips, you might feel your mouth drying out and have a nice long drink of water. When you do this, you are moving water from a region of high concentration (your glass or water bottle) to a region of low concentration (your salty mouth). Keep in mind though, that in this case the water isn’t actually diffusing across a membrane; instead, you are actively moving it from glass to mouth.
Negative numbers for water potential can be confusing. Just remember that if a negative sign is in front of a number, it is just as far away from zero as the positive version of that number. -10 is less than -1, and -1 is less than 3.
Stomata aren’t cells. They are pores, or holes, in the leaf surface. However, they are always accompanied by two guard cells, which regulate their opening and closure.
The female parts are called carpels, and are made up of SOSO: style, ovaries, stigma and ovules. The male parts are called stamens and is made up of AF: anthers and filaments.
What is a fruit and what is a vegetable? We just told you that fruits develop on plants and protect seeds, but what about cucumbers, tomatoes, and eggplants? The food pyramid says we should eat fruits and vegetables, but botanically speaking, the things we call vegetables are actually fruits (if you look inside, you’ll find seeds in them). For our purposes here, there is no such thing as a vegetable. Try using that line at the dinner table. There is, however, vegetative tissue, which is any part of the plant that doesn’t contribute to reproduction.
Germination and Development
Hypocotyl vs. epicotyl: the key to keeping these straight is breaking the words down. "Cotyl" refers to the cotyledons. "Hypo" means below, so the hypocotyl is the region of the stem below the cotyledons. "Epi" means above, so the epicotyl is the region of the stem above the cotyledons.
The dark period has an important influence on flowering, but the influence is different for short day plants and long day plants. Dark periods promote flowering in short day plants, but inhibit flowering in long day plants. A good way to keep this straight is to remember that short day plants need short days and long day plants need long days. But that’s just the definition of those names, right? Since each "day" takes place in a 24-hour period, the time that doesn’t have daylight is dark. So short days have long nights, which is exactly what short-day plants need; long days have short nights, which is exactly what long day plants need.
Auxin, cytokinins, gibberellins and ethylene are all involved in growth. Abscisic acid is the odd man out, because it inhibits growth.
Abscisic acid (ABA) has a name that implicates it in the abscission of leaves and fruits. However, ABA is much more important in dormancy and drought stress than it is in abscission—don’t let the name fool you.
Even though Charles and Francis Darwin’s experiment led to the discovery of auxin, don’t forget that Charles Darwin is most famous for his theory of evolution by natural selection.
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