CHARACTERISTICS OF
PROKARYOTIC AND
EUKARYOTIC CELLS
Introduction
All living organisms are made of
basic functional units called cells.
There are two main types of cells
- prokaryotic and eukaryotic. Let's
examine the key differences
between their structures and
transport mechanisms.
Prokaryotic Cell Structure
Prokaryotic cells include bacteria
and lack membrane-bound
organelles. Some key points:
Cell Size and Shape
Typically smaller than
eukaryotic cells, around 1-
10 micrometers
Often take rod-like (bacilli),
spherical (cocci) or spiral
(spirilli) shapes
May occur singly or in
characteristic groupings
Cell Envelope
Rigid cell wall made of
peptidoglycan provides
structure and shape
Outer membrane present in
gram-negative bacteria
Glycocalyx layer exterior to
cell may act as capsule or
slime layer
Internal Structures
Chromosomal DNA located
in nucleoid region of
cytoplasm
Ribosomes for protein
synthesis
Some may form hardy
endospores during
starvation
Appendages
Flagella or pili help in
motility, attachment and
genetic exchange
Transport Across Membrane
Passive diffusion, facilitated
diffusion, osmosis
Active transport against
concentration gradients
Group translocation of some
molecules
Eukaryotic Cell Structure
Eukaryotic cells have more
complex, compartmentalized
structures:
Internal Membranous
Structures
Nucleus surrounded by a
nuclear envelope and
containing chromosomes
Variety of membrane-bound
organelles for specialized
functions
Cell Covering Structures
Plant cells have rigid
cellulose cell walls
Fungi may have chitin or
cellulose cell walls
Animal cells lack cell walls
Organelles
Mitochondria - sites of
aerobic respiration and ATP
production
Chloroplasts -
photosynthesis in plants
Endoplasmic reticulum -
protein and lipid synthesis
Golgi apparatus -
modification, packaging and
secretion
Lysosomes - enzymatic
digestion
Cytoskeleton
Microfilaments and
microtubules contribute to
shape, movement etc.
Transport Across Membrane
Passive diffusion, facilitated
diffusion, osmosis, active
transport
Vesicle-mediated transport
e.g. endocytosis,
phagocytosis
A MULTIDIMENSIONAL PERSPECTIVE ON COGNITIVE AGING
I. Understanding Primary Aging
Primary aging refers to normal, inevitable age-related changes in cognition
It is considered healthy and non-pathological
Occurs through biological processes like neuronal loss, decreased processing speed
Affects networks throughout the brain rather than localized regions
Slowing of processing speed is a hallmark characteristic
This impacts functions highly dependent on speed, such as:
Problem solving - taking longer to analyze situations and weigh options
Executive functions - requiring quick multitasking, flexibility, planning
Timed tests that evaluate these domains may show greater decline
However, not all primary aging results in impairment
Some experience "usual" aging with steady decline
Others experience "successful" aging through neutral/positive lifestyle:
Regular physical/mental activity
Rich social engagement
Absence of chronic health conditions
II. Secondary Aging and Health Conditions
Secondary aging refers to age-related changes due to illness/disease
Adds an additional layer of cognitive impacts beyond primary aging
Diseases become more prevalent with advanced age
Conditions like cardiovascular disease, diabetes, can negatively influence cognition
Of greatest concern is dementia, severely damaging memory and thinking abilities
Dementia prevalence increases drastically as a function of age
Early diagnosis is challenging as changes may mimic normal aging
III. Distinguishing Primary vs. Secondary Aging
As people age, it gets increasingly difficult to separate the two influences
No consensus on where to draw the line between normal vs. pathological aging
At older ages, they likely interact in complex ways producing a mixed clinical picture
Risks of overdiagnosis, such as labeling normal forgetfulness as dementia
Risks of underdiagnosis also exist by dismissing mild impairments
Ongoing challenge is detecting underlying degenerative processes
IV. Impact of Sociocultural Context
Environmental context impacts adult development and cognitive demands
Cohort effects associate abilities with modern life experiences of that generation
Period effects link to opportunities/expectations of historical time period
Daily activities pose fewer mental demands later in life for many
Challenges may not be detected on tests if daily functioning remains intact
V. Accounting for Everyday Cognitive Demands
Most neuropsychological tests have no real-world analog
They capture performance under standardized laboratory conditions
But real challenges involve multitasking, distractions in natural settings
Need to understand how well people manage complex daily living skills
Relating test scores to functioning in familiar routine activities
VI. Memory and Intellect Across Adulthood
Provide lifespan perspective considering both stability and changes
Memory normally shows decline, especially episodic/recall abilities
Yet semantic knowledge often remains well-preserved
Intellectual abilities tend to remain intact or experience little change
Vocabulary, general knowledge frequently hold steady into late life
Individual factors like education, occupational complexity influence reserve
VII. Principles of Multidimensional Assessment
Consider full range of cognitive strengths and weaknesses
Evaluate underlying mechanisms responsible for patterns of performance
Situate abilities within personal sociocultural-historical context
Recognize complex interacting influences of aging process
Give fair differentiation of normal from pathological presentation
Multitude of overlapping factors shape cognitive changes with age
Accurate evaluation balances numerous dimensions simultaneously
