Notes, summaries, assignments, exams, and problems for Biology

Key Characteristics of the Animal Kingdom

• Multicellular with differentiated tissues and organs
• Eukaryotic cells
• Heterotrophic: Feed on other living things
• Motile: Capable of active movement
• Sensitive to environmental changes
• Possess an internal or external skeleton
• Found in aquatic and terrestrial environments

Invertebrates and Vertebrates

• Invertebrates: Do not possess a spinal column (e.g., butterflies, sea urchins).
• Vertebrates: Possess a spinal column (e.g., cats, frogs).

Types of Body Symmetry

• Radial Symmetry: Body parts arranged around a central axis (e.g., starfish).
• Bilateral Symmetry: Body can be divided into two mirror-image halves (e.g., insects, vertebrates).

Animal Feeding Strategies

Dietary Classifications:

• Carnivores
• Herbivores
• Omnivores

Specific

Characteristics of Poriferans

Poriferans, also called sponges, are aquatic organisms (the majority of them are marine organisms) that either have no symmetry or have radial symmetry. Their bodies, which have a tube shape, a cup shape, or an irregular shape, have multiple pores that are interlinked by thin channels. These channels lead to a central cavity, called the atrium, which is linked to the outside by an opening called the osculum. Inside the channels, there are cells known as choanocytes, which are specialized in capturing food.

Poriferans stay upright due to a skeleton made of small spines called spicules. They feed by filtration. Water, which contains food particles, enters through the pores and exits through the osculum with the food...

1. Essential Atmospheric Layers

The troposphere and the stratosphere are the most important layers for life. The atmospheric structure includes:

• Troposphere: The lowest layer (contains the tropopause and ozone maximum).
• Stratosphere: Located above the troposphere.
• Mesosphere: Includes the mesopause.
• Thermosphere: The highest layer.

2. Primary Atmospheric Gases

The atmosphere is composed mainly of Nitrogen (78.9%) and Oxygen (20.95%). Other trace gases include:

• Argon: 0.93%
• CO2: 0.038%
• Traces of neon, helium, methane, water vapor, krypton, hydrogen, xenon, and ozone.

3. Climate Influencing Factors

The two abiotic factors that influence climate the most are temperature and moisture.

4. Solar Radiation Distribution

Solar radiation reaching Earth is either reflected...

The Sense of Hearing and Balance

The sense of hearing is located inside the ears. Sounds are vibrations of the air, received by the eardrum. The eardrum transfers these vibrations to the cochlea, where mechanoreceptors transform them into nerve impulses. These impulses then travel to the brain through the auditory nerve. The sense of balance is also located inside the ear and is closely related to the sense of hearing.

The Organization of the Nervous System

The nervous system is composed of two main divisions: the Central Nervous System (CNS) and the Peripheral Nervous System (PNS).

Central Nervous System (CNS)

• The Central Nervous System (CNS) comprises the brain and the spinal cord. This is where all stimuli are evaluated, and responses are generated.

Genetic Code

• Each codon or triplet codes for a specific amino acid.
• It is degenerate: Amino acids can be coded by more than one codon or triplet (some triplets are synonyms). There are 64 codons for 20 amino acids.
• It is not ambiguous: Each codon encodes only one type of amino acid.
• It is universal: Apart from a few small exceptions.
• There are triplets that determine the beginning of translation ('start codon'): AUG (It codes for the amino acid methionine - Met).
• There are triplets that determine the end of translation ('termination' or 'stop' codons): UAA, UAG, UGA (They do not code for any amino acids).

Chromosomes

They are stick-shaped structures that arise from the condensation and packaging of chromatin during the division phases (mitosis and...

• In the case of partial injuries, some sensation and movement may be retained below the level of the injury.

• In complete injuries, there is a loss of sensation and total muscular paralysis below the level of the injury

• Depression is a mental illness that often takes the form of low mood and an inability to lead a normal life

Functions of the Blood

Transports nutrients and oxygen to all the cells and collects waste products produced by cell metabolism. Contributes to the regulation of body temperature. Plays a role in the fight against infections.

Cardiovascular System

Shares nutrients and oxygen between cells and collects waste products that cells produce during metabolism.

Key Properties of Proteins

• Their molecular weight ranges from 1,000 to several hundred thousand.
• Generally water-soluble, with the exception of hydrophilic membrane proteins.
• Absorb light in the UV range, with maximum absorption at 280nm due to the presence of aromatic amino acids.
• Have a specific isoelectric pH (pI). Positively charged below pI, negatively charged above pI.
• Proteins are charged, which depends on the buffer.
• Move under the electric charge and can be separated by electrophoresis.
• Give a color reaction with reagents, such as a blue color with ninhydrin.

Classification of Proteins

Basis of Structure

1. Globular: All enzymes and intracellular proteins are globular, such as myoglobin and hemoglobin.
2. Fibrous: Mostly extracellular, such as collagen.

Human Nutrition

The cells of all organisms require nutrients to grow and function. Heterotrophic organisms, like humans, cannot produce their own nutrients, so they obtain them from food. Multicellular organisms have many organs grouped into systems, such as the digestive and respiratory systems.

Digestive System

Like all animals, humans obtain proteins, fats, and sugars from food through the digestive system. Food processing involves three phases: digestion, absorption, and waste expulsion. Food moves through the digestive tract via peristaltic movements—muscle contractions in the tract walls that narrow the tube.

Respiratory System

Besides nutrients from digestion, our cells need oxygen for cellular respiration, the process that converts glucose...

Ova Formation (Oogenesis)

Oogenesis takes place in the ovaries:

• Stage one: Females develop immature ova when they are embryos inside their mother's womb. These ova are surrounded by cells called follicles. The ova stop developing until puberty.
• Stage two: After puberty and until menopause, in cycles of approximately 28 days, one follicle grows, the ovum matures, and the ovum leaves the ovary (ovulation).

Formation of Spermatozoa (Spermatogenesis)

Spermatogenesis occurs in the male reproductive tract:

• It occurs in the walls of the seminiferous tubules, which contain germ cells that multiply.
• Spermatozoa move to the lumen of the tubule and mature.

Female Reproductive System: Functions and Parts

Functions

• Manufactures female gametes (ova).
• Provides a place