Biology by Himani Sharma

Balance by the Vestibular Apparatus (Labyrinth)
The vestibular apparatus consists of:
Utricle
Saccule
Three semicircular canals
These structures maintain equilibrium (balance).
A. Static Balance (Head Position)
Maintained by the Utricle and Saccule.
These contain sensory patches called maculae.
Above the hair cells is a jelly-like layer containing tiny calcium carbonate crystals called Otoconia (Otoliths).
What are Otoconia?
Tiny crystals of calcium carbonate (CaCO₃)
Also called ear stones or otoliths
They add weight to the gelatinous membrane.
How do they work?
When you:
tilt your head,
bend forward,
stand up,
or move in a straight line,
gravity causes the otoconia to shift.
This movement bends the hair cells, producing nerve impulses that tell the brain the position of the head.
Remember:
Otoconia = Gravity sensors.
B. Dynamic Balance (Rotational Movement)
Maintained by the three semicircular canals.
Each canal has an enlarged region called the ampulla, containing the crista ampullaris (hair cells).
Mechanism
When you rotate your head:
The fluid (endolymph) lags behind because of inertia.
It bends the cupula and hair cells.
Hair cells generate nerve impulses.
The brain detects the direction and speed of head rotation.

1. Low to moderate estrogen level → Negative feedback
During most of the menstrual cycle:
Developing ovarian follicles secrete low to moderate amounts of estrogen.
This estrogen acts on the hypothalamus and anterior pituitary.
It decreases:
GnRH secretion from hypothalamus
FSH and LH secretion from anterior pituitary
Purpose:
To prevent excessive stimulation of many follicles and allow only the dominant follicle to continue developing.
2. High estrogen level for a sustained period → Positive feedback
Near the middle of the cycle (around day 12–14):
The dominant follicle becomes mature.
It secretes a very high level of estrogen (estradiol).
This high estrogen concentration is maintained for about 36–48 hours.
Now estrogen changes its effect:

Anterior pituitary releases a large amount of LH (and some FSH)
This sudden rise in LH is called the LH surge.
Why does high estrogen switch to positive feedback?
The body interprets prolonged high estrogen as a signal:
"The follicle is mature and ready for ovulation."
Therefore, instead of suppressing reproduction, the brain activates the reproductive axis to trigger ovulation.

Think of a room with green wallpaper covered by a yellow curtain.
Y gene = Someone pulls down the yellow curtain by hiding the green wallpaper so you see yellow.
y gene = Nobody pulls down the yellow curtain so the green wallpaper is visible, so the room stays green.
So, yellow is an active process (chlorophyll breakdown), whereas green is the default state when that process does not occur. This is why the green allele is recessive.

"What if I told you that the tiny Golgi apparatus inside your cells helped scientists win a Nobel Prize?"

"Every second, millions of proteins travel inside your cells like courier packages.
But who decides where each package goes?
The answer lies in cell trafficking.
Proteins are made in the rough ER, then sent to the Golgi apparatus.
The Golgi acts like Amazon's sorting hub— it modifies proteins, attaches molecular address tags, packs them into vesicles, and dispatches them to their exact destination.
Without this traffic system, hormones, enzymes, neurotransmitters—even insulin—would never reach where they're needed."

"In 2013, the Nobel Prize in Physiology or Medicine was awarded to James E. Rothman, Randy W. Schekman, and Thomas C. Südhof for discovering how this cellular transport system works—one of the most fundamental processes of life."
"So remember—Golgi isn't just an organelle in your NCERT. It's the world's most efficient microscopic logistics company... and understanding it earned a Nobel Prize!" 🧬📦✨

A lichen is not a single organism—it's a symbiotic partnership between:
A fungus, which provides structure, protection, and absorbs water and minerals.
A photosynthetic partner (either an alga or a cyanobacterium), which makes food through photosynthesis.
Together, they form a stable organism that can survive in environments where many other life forms cannot.
There are three main growth forms:
Crustose: Thin, crust-like, tightly attached to rocks or bark.
Foliose: Leaf-like, with lobes that are loosely attached.
Fruticose: Shrubby or branching, often hanging from trees.

Vector-mediated transformation (using plasmids/phages):
The origin of replication (ori) is required if the introduced DNA is expected to replicate independently inside the host cell. Without an ori recognized by the host, the plasmid cannot replicate and will eventually be lost.
Direct gene transfer (electroporation, microinjection, gene gun, etc.):
The ori is generally not required because the transferred DNA is usually integrated into the host chromosome or expressed transiently. Once integrated into the chromosome, the host's own chromosomal origin of replication replicates the inserted gene along with the rest of the genome.

Screening of Recombinant Transformed Cells
"Let's understand Method I – Insertional Inactivation of Antibiotic Markers for screening recombinant transformed cells.
After the transformation process, there are three possibilities.
Possibility A represents a non-transformant. These cells do not receive any plasmid, so they are sensitive to both Ampicillin and Tetracycline. As a result, they do not grow on either antibiotic plate.
Possibility B represents a non-recombinant transformant. These cells receive the original plasmid without the desired gene. Therefore, both the Ampicillin resistance gene and Tetracycline resistance gene remain functional. These colonies grow on both Ampicillin and Tetracycline plates.
Possibility C represents the recombinant transformant, which is our desired cell. Here, the foreign DNA is inserted into the Tetracycline resistance gene, inactivating it. This process is called insertional inactivation. As a result, these cells are resistant to Ampicillin but sensitive to Tetracycline. They grow only on the Ampicillin plate and fail to grow on the Tetracycline plate.
Now, let's see how selection is done.
First, colonies are grown on a master plate. Using replica plating, the same colony pattern is transferred onto two separate plates—one containing Ampicillin and the other containing Tetracycline.
After comparing both replica plates with the master plate, the colony that is present on the Ampicillin plate but absent on the Tetracycline plate is identified as the recombinant transformant.
Finally, that colony is picked from the master plate, because the original colony is still alive there, and it is cultured separately for further applications.
This is how insertional inactivation helps us identify recombinant cells accurately.